IntroductionAdults have the power to support children’s autonomy, or their sense of control over their own life1. Children’s sense of autonomy develops early2 and age-appropriate autonomy is necessary for healthy development3. Adults often decide what level of autonomy is age-appropriate based on their understanding of child development3. However, there may be differences in adults’ understanding of the gender development of transgender youth4 (i.e., whose gender identity and expression do not align with that expected based on their sex assigned at birth) versus cisgender youth (i.e., whose gender identity and expression align with that expected based on their sex assigned at birth). Such differences may reflect in views on when transgender youth should achieve gender identity autonomy. Simultaneously, a legal movement that seeks to limit the autonomy of transgender youth is taking place within all three branches of the United States government. For example, a January 2025 executive order limited transgender people’s civil rights, protections, and legal recognition5, and in June 2025, the U.S. supreme court upheld a state-level ban on gender-affirming care (i.e., social, psychological, medical, and behavioral interventions supportive of one’s gender identity) for transgender teenagers in Tennessee6, potentially shielding similar laws in other U.S. states. And, in the 2025 legislative session, 616 bills were considered that proposed to limit transgender youth’s autonomy by reducing access to gender-affirming care and restricting rights7.Past work has identified various predictors of support for anti-transgender legislation that seeks to limit transgender youth’s autonomy. For example, negative implicit and explicit attitudes toward transgender people predict support for anti-transgender policies8, including policies that exclude transgender women from spaces for women9,10. Additionally, support for anti-transgender legislation is associated with greater endorsement of essentialist views of gender, conservatism, and religiosity11. One underexplored contributor to this desire to limit transgender youth’s autonomy is adults’ perceptions of how gender identity develops.Thus, this work examined how adults’ perceptions of gender identity development contribute to support for children’s autonomy to identify and express their own gender. We conceptualize adults’ understanding of gender development as related to but separate from prejudiced attitudes against transgender people. We first tested whether adults believe that gender development occurs later in transgender youth than cisgender youth (Study 1), and second, whether this tendency predicts support for children’s gender identity autonomy and subsequently for autonomy-limiting anti-transgender legislation (Study 1). Finally, this work tested whether increasing adults’ understanding of gender development can predict increased support for children’s gender identity autonomy and thus decreased support for anti-transgender legislation (Studies 2 and 3) and increased behavioral support for the rights of transgender youth (Study 3).Lay understanding of gender developmentMost adults have a limited understanding of child development and estimate that youth reach developmental milestones later than research finds, such as performing simple cognitive and perceptual motor tasks (e.g., knowing their age, copying a square), processing race12, or learning about LGBTQ+ topics13. This tendency impacts when adults are willing to discuss certain topics with youth—adults who give older estimates of when children begin to process race are more likely to delay conversations about race because they believe youth do not have the capacity to understand14, and parents who believe LGBTQ+ topics are not age-appropriate are less likely to discuss these topics with their children13.While adults may tend to give older estimates of developmental timing in general, this may be exacerbated in their perceptions of gender development, particularly for that of transgender youth. We suggest adults may believe transgender youth reach gender development milestones later than cisgender youth, despite empirical research demonstrating many similarities between the gender development of transgender youth and cisgender youth15,16,17,18,19. Many youths conform to adults’ common expectations about gender—namely, that gender identity and expression align with that expected based on sex assigned at birth. In contrast, when transgender youth do not conform with these expectations, this variation from what is considered “typical” development is salient and adults may anticipate additional differences between the gender development of transgender children and cisgender children20. Indeed, transgender youth and adults are stereotyped as not knowing their own gender21, while cisgender youth and adults are not. Moreover, adults often view gender nonconformity as temporary, or experience shock at a child disclosing a transgender identity, underscoring that transgender identities may be unexpected and challenged22,23,24. In contrast, adults expect and support youth’s gender conforming behavior, or cisgender identity expression25.Expectations about gender development and autonomy supportAdults’ understanding of child development is critical because adults decide what is developmentally appropriate for youth. When these decisions are based on older estimates of when youth reach developmental milestones, youths’ autonomy may be inappropriately restricted. Autonomy support from parents is necessary for healthy identity development in childhood and adolescence3,26, including the development of transgender youths’ identities, and mental and physical health27,28,29,30. Adults’ beliefs about the gender development of transgender youth have been linked to transgender youth’s autonomy. In a qualitative study, 14- to 18-year-old transgender teenagers cited others’ questioning of their ability to know their own gender as a barrier to receiving hormone therapy31. Further, some youth felt that their healthcare providers underestimated how much they had thought about treatments like hormone therapy. As gender-affirming care is medically necessary and can be lifesaving for transgender youth32,33,34,35,36, this demonstrates that inappropriate restrictions to autonomy driven by a belief that transgender youth reach gender development milestones later than cisgender youth can have serious and lasting consequences.Current studiesThe current studies focused on support for anti-transgender legislation and rights of transgender youth, as arguments for anti-transgender legislation in the U.S. purport that transgender youth are too young to make decisions about their identities and bodies. We tested whether adults believe transgender youth meet gender development milestones at later ages than cisgender youth, and whether this difference in perceptions of gender development predicts support for youth’s gender identity autonomy and thus for autonomy-restricting anti-transgender legislation (Study 1). We predicted that participants would believe transgender youth reach important milestones in their gender development at later ages than cisgender youth.Studies 2 and 3 tested whether an educational intervention designed to increase knowledge about transgender youths’ and cisgender youths’ gender identity development reduced the difference in participants’ perceptions of gender development for transgender youth relative to cisgender youth. Both studies also tested whether reducing this difference in perceptions of gender development would predict greater support for youths’ gender identity autonomy and lower support for anti-transgender legislation (Studies 2 and 3) and/or stronger behavioral support for transgender rights (Study 3). Specifically, we predicted that perceptions of gender development and autonomy support would serially mediate the relation between the intervention and support for anti-transgender legislation and behavioral support. Of note, rather than participants’ accuracy, this work assesses relative differences in participants’ beliefs about the gender development of transgender children compared to cisgender children. Though data on the gender development of transgender children is increasing, it is still relatively limited and drawn primarily from retrospective reports of families who support their child’s transition, e.g.37.MethodsThe methods, research questions, planned sample size, inclusion/exclusion criteria, and analysis plan for each study were preregistered before data collection in 2023 (Study 1: 4/21/2023, https://osf.io/dhjq6), and 2024 (Study 2: 3/1/2024, https://doi.org/10.17605/OSF.IO/GQPJX; Study 3: 5/24/2024, https://doi.org/10.17605/OSF.IO/GSPMW). All studies received ethical approved by the Institutional Review Board at Northeastern University.ParticipantsParticipants were adults living in the United States recruited online either through Prolific (Studies 1 and 3) or via NORC (Study 2) between 04/21/2023 and 05/28/2024. Final samples included N = 200 participants in Study 1 (113 men, 79 women, 4 non-binary, 2 transgender, 2 prefer another term; Mage = 36.7 years, SDage = 13.9; 71% white, 9% Multiracial, 7% Asian, 5% Latina/o/x, 4% Black, 2% prefer to self-identify, 1% prefer not to say/missing,