Has there been research on the impact of gay parents on the sexual orientation of adopted children? Disclamer: I am not interested in personal views on whether gay parenting is a good or bad thing. I would like to understand whether there has been serious research on the upbringing consequences for such children. I am a physicist so I know nothing about psychology, but I am good with numbers and their statistical interpretation so anything substantiated is very much welcome. Thank you
Gay parenting, whether official or not, is in place for now more than a generation and among the fierce debates about that topic (I am French), I tried to look for research that would bring some actual data on the comparative measurable effects of gay vs straight parenting (on the children). The point I am interested in is specifically the sexual orientation of the children (now grown-ups).
I did not find anything substantial, probably because I do not know the right literature in that field.
Is there such research?
Farr, R. H., Forssell, S. L., &amp; Patterson, C. J. (2010). Parenting and child development in adoptive families: Does parental sexual orientation matter?. Applied Developmental Science, 14(3), 164-178. https://doi.org/10.1080/10888691.2010.500958
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This study investigated child development and parenting in 106 families headed by 27 lesbian, 29 gay, and 50 heterosexual couples (80% White, M = 42 years) with young adopted children (41% White, M = 3 years). Parents and teachers reported that, on average, children were developing in typical ways. Measures of children's adjustment, parenting approaches, parenting stress, and couple relationship adjustment were not significantly associated with parental sexual orientation. However, several family process variables—parenting stress, parenting approaches, and couple relationship adjustment—were found to be significantly associated with children's adjustment, regardless of parental sexual orientation.

Herek, G. M. (2014). Evaluating the methodology of social science research on sexual orientation and parenting: A tale of three studies. UCDL Rev., 48, 583. https://heinonline.org/HOL/LandingPage?handle=hein.journals/davlr48&amp;div=18&amp;id=&amp;page=
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For at least four decades, questions about the well-being of children raised by sexual minority individuals or same-sex couples have figured prominently in public debates about adoption, foster parenting, child custody and visitation, and marriage equality. Those debates have often focused on questions of law, personal values, and morality, but many have also included empirically testable assertions about the relationship (or lack thereof) between parents' sexual orientation and their children's developmental outcomes. The social science research that has empirically assessed the validity of those assertions is the focus of the present paper.

Patterson, C. J. (2017). Parents' sexual orientation and children's development. Child Development Perspectives, 11(1), 45-49.  https://doi.org/10.1111/cdep.12207

What if any influence does parents' sexual orientation have on children's development? Research suggests that, contrary to concerns voiced by many observers, parents' sexual orientation has little if any direct impact on children's development. Even so, some distinctive qualities of experiences in families of lesbian and gay parents have been noted, and their implications are not fully understood. Moreover, research on individual differences among families headed by lesbian mothers and gay fathers, and their possible impact on children, is still in its early phases. In this article, I provide an overview of research in this area and offer suggestions for further studies.

Stacey, J., &amp; Biblarz, T. J. (2001). (How) does the sexual orientation of parents matter?. American Sociological Review, 159-183. https://doi.org/10.2307/2657413

Opponents of lesbian and gay parental rights claim that children with lesbigay parents are at higher risk for a variety of negative outcomes. Yet most research in psychology concludes that there are no differences in developmental outcomes between children raised by lesbigay parents and those raised by heterosexual parents. The analysis here challenges this defensive conceptual framework and analyzes how heterosexism has hampered intellectual progress in the field.