Hearing relatives describe the same childhood in sharply different ways is common — one brother remembers a warm, adventurous upbringing while a sister recalls strict rules and missed opportunities. New popular coverage and decades of behavioural-genetics research say this is not just family myth-making but a predictable result of how children experience the world differently even under one roof. A recent explainer in HuffPost lays out the clinical and practical reasons siblings can have vastly different childhoods, from changing family circumstances and parental moods to birth order and personality differences HuffPost. That observation aligns with long-standing scientific work on the “nonshared environment” — the environmental influences that siblings do not share — and has direct implications for Thai families navigating shrinking household sizes, rapid economic change and shifting gender and filial expectations.
The idea matters because memories of childhood shape adult relationships, mental health and family cohesion. If siblings’ recollections diverge sharply, old wounds and questions of fairness can linger. Researchers in behavioural genetics long ago showed that genes plus nonshared environmental effects explain why siblings within the same family often differ as much as unrelated people raised apart. Leading reviews and commentaries summarise the evidence that most environmental effects on personality and psychopathology are, in fact, nonshared — meaning what happens uniquely to one child (a bullying episode at school, a warm teacher, a parental illness during their formative years) can leave lasting differences International Journal of Epidemiology review; PubMed and commentary on nonshared environment. Recent work reinforces that many of these influences are idiosyncratic and sometimes effectively random from the family’s perspective Plomin, 2024.
Several key mechanisms explain why siblings raised together may narrate different childhoods. One is that family circumstances change over time. As the HuffPost piece notes, a family’s finances, parental relationships, work demands and social supports often shift between the births of the first and later children; that can change access to activities, schooling or how much time parents have for one child versus another HuffPost. Clinical psychologists quoted in that story emphasise that parents’ emotional bandwidth — affected by sleep, stress, mental health, partnerships and work — often differs across pregnancies and child-rearing stages, which naturally alters caregiving and discipline. Parents can become more relaxed or more exhausted with later children; some correct approaches used with an older sibling or react differently to a child’s temperament, producing different lived experiences.
Birth order and role expectations form a second pathway. Older siblings commonly carry more responsibility, act as caretakers, and face higher expectations; younger children may grow up under more confident parents but with less direct attention. That difference in roles can create distinct memories about fairness and burden. Research on birth order and sibling roles in Asian contexts shows similar patterns — eldest children often report more family responsibility and caregiving duties, and cultural expectations can shape how brothers and sisters view those responsibilities Perceptions of sibling relationships and birth order among Asian youths.
Personality and temperament are a third major reason. Parents respond to each child’s unique traits: an easygoing child may receive more positive reinforcement, while a highly sensitive or strong-willed child may trigger stricter control or more exhaustion in caregivers. Practitioners quoted in HuffPost put it plainly: “All siblings are unique individuals — including twins,” and parents naturally adapt parenting to child temperament, which can look like unequal treatment though it may be an equitable attempt to meet different needs HuffPost. Behavioural-science reviews call this “evocative” effects of personality on parenting — children’s traits evoke different responses from their environment, including parents and teachers behavioural genetics literature.
Nonfamily outside influences — peers, teachers, coaches and chance events — also create rifts in siblings’ memories. A child who finds a supportive teacher or a single close friend can have a more positive school experience than a sibling who was bullied or overlooked. Plomin and colleagues summarise decades of twin and family studies showing that much of what shapes long-term differences between siblings are these nonshared external experiences (for example, a unique peer group or a pivotal incident) rather than the shared household environment itself behavioural-and-brain-sciences review.
All these mechanisms are supported by accumulated empirical work. Classic studies and more recent reviews conclude that shared family environment explains surprisingly little of the lasting differences in personality and mental health among siblings; instead, genes plus nonshared environmental effects — many of them unique experiences or even measurement error in how we recall events — explain the variance Plomin & Daniels; nonshared environment literature review. A recent 2024 discussion argues that while nonshared environmental effects are real, they can be “random” and hard to pin down for interventions, which is why families can find it frustrating when siblings’ experiences diverge without an easy explanation Plomin, 2024.
For Thai families the scientific findings intersect with local demographic and cultural trends that make sibling differences especially salient. Thailand’s fertility rate has fallen sharply over recent decades, with many couples now having one or two children rather than larger households; this means generational spacing, solo-child households and significant life-course timing differences across siblings are increasingly common Thailand MICS 2022 report (NSO/UNICEF) and Statista fertility data. Smaller families and late parenthood alter the conditions into which each child is born: a firstborn arriving when parents are young and under financial strain might face very different material and emotional circumstances than a younger sibling born after career and economic change. Rural-to-urban migration, internal labour mobility and international employment of parents (common in many Thai households) further fragment siblings’ upbringing: a child left behind in a village may grow up with extended family caregivers while a younger sibling grows up in a Bangkok condominium with different schools and social opportunities research on Thai family structure and intergenerational transfers.
Thailand’s cultural norms also shape how differential treatment is perceived. Strong expectations around filial piety, respect for elders and gender roles can magnify the emotional weight of unequal experiences. Studies in Southeast Asian contexts show that eldest children — especially daughters — may inherit household responsibilities and educational trade-offs, producing life trajectories different from their siblings birth order research in Asian samples. That can translate to adult disputes about perceived unfairness in childhood investment, especially in education or migration opportunities.
What should Thai parents and adult siblings take from this research? First, unequal childhoods do not automatically signal parental malice or neglect. As multiple psychologists quoted by HuffPost emphasise, “children do not have to be treated exactly the same at all times to be treated equitably,” because each child has different needs and contexts HuffPost. Second, differences that cause ongoing pain — long-held resentment, mental-health impacts, or family estrangement — benefit from open communication and, when needed, professional help. Experts suggest allowing space for each sibling to describe their experience without defensive rebuttal, as that fosters perspective-taking and repair HuffPost.
Practically, Thai families can take several concrete steps informed by the science:
Normalize divergent memories. Parents can explain how family circumstances changed over time (economic ups and downs, new jobs, parental health) so adult children understand why things were different. That context often reduces the sting of perceived unfairness. The behavioural-genetics literature supports contextualizing differences as an expected product of life-course change rather than moral failing nonshared environment review.
Avoid simple comparisons. Instead of telling children “I treated you both the same,” parents can describe how they tried to meet each child’s needs differently. Parenting educators emphasise specificity: parents explaining why a different approach was taken (for example, extra discipline when a child was at risk, or flexibility to protect emotional needs) can help siblings accept difference as intentioned rather than preferential HuffPost.
Encourage sibling conversations with rules: one person speaks at a time, no interruptions, no defensive rebuttals, and focus on how experiences felt rather than on blaming motives. If conversations become heated, a neutral facilitator — a family counsellor or community elder — can help.
Seek professional help when memories create distress or impair relationships. Thailand’s mental-health infrastructure has been strengthening: the country operates a 24-hour Mental Health Hotline (1323) integrated into universal health coverage, and national services are expanding crisis and counselling capacity WHO profile of Thailand’s suicide-prevention work referencing hotline 1323 and NHSO integration of a mental-health hotline. Local community resources such as the Bangkok Community Resources crisis page list additional contacts for urgent help and counselling supports Bangkok Community Resources crisis page.
For parents-to-be or parents raising young children, consider keeping a simple family timeline or journal that records major life changes and decisions about schooling, moves and caregiving. That information can later help adult children and therapists understand why siblings experienced different opportunities.
Schools and health professionals can add sibling history questions into routine family assessments — asking not just about “the family” but about birth order, parental employment at the time of each child’s early years, and significant life events — to better tailor support services.
Looking ahead, social and demographic trends will make nonshared childhoods more common and visible in Thailand. Continued fertility decline, later parenthood, increased female labour-force participation and uneven internal migration mean children increasingly enter family life at different junctures in parents’ careers and relationships. The digital divide and uneven access to quality schooling — accelerated by the COVID-19 pandemic — can also create divergent educational experiences within one family, especially where older siblings were in school-age years during closures while younger ones were not. Those structural shifts mean policymakers and service providers should expect greater within-family inequality in experiences and plan supports accordingly.
At the same time, the research also points to limits on parental control: some nonshared influences are chance events or peer interactions that are difficult to prevent. That should free parents from guilt about making every decision perfectly equal and shift the focus toward creating safe, open family systems where differences can be discussed and repaired. Interventions that build parental mental-health supports, reduce economic shocks, and strengthen school climates will lower the risk that nonshared adverse experiences become persistent disadvantages.
For Thai readers seeking practical next steps today: start a family conversation that invites each sibling to describe, without interruption, one memory that shaped their view of childhood. Parents can acknowledge changes (job moves, separations, illness) that explain material differences. If conversations reveal deeper hurt, consider family therapy or individual counselling; call the 1323 mental-health hotline for guidance on local services and referral options NHSO mental-health hotline integration. Schools and community clinics can help mediate sibling disputes and provide supportive programs that acknowledge children’s differing experiences.
The science and expert commentary converge on a humane conclusion: siblings who remember different childhoods are not anomalies but normal outcomes of complex, evolving family lives. Understanding the roles of shifting circumstances, birth order, personality and chance makes it easier for Thai families to move from judgment to dialogue. That shift — from defending memories to listening and contextualising them — is the clearest path toward repairing rifts, reducing resentments and turning divergent childhoods into shared, understood family histories.
Sources cited in this report include the HuffPost feature summarising clinician insights and interviews (HuffPost, 2025) HuffPost; classic and review literature on nonshared environment and why siblings differ International Journal of Epidemiology review and PubMed summary and PMC commentary on nonshared environment; a recent discussion of nonshared environmental effects Plomin, 2024; research on sibling relationships and birth order in Asian contexts PMC article on perceptions of sibling relationships; demography and household data for Thailand Thailand MICS 2022 full report (NSO/UNICEF) and fertility data Statista; and information on mental-health hotline services and national efforts in Thailand WHO profile and NHSO announcement on hotline 1323 and NHSO integration announcement. Additional academic discussion of sibling differences can be found in behavioural-science reviews Cambridge/BBS review.