Adoption: Yichud & Affectionate Contact

 https://outorah.org/p/160720/

Rabbi Moshe Feinstein is also among those who rule leniently on the issue of Yichud and adopted children, however his reasoning for doing so is especially unique and innovative.[6] He insists that no adoptive father would commit any sexual impropriety with an adopted daughter, for fear of being caught by his wife. Rabbi Feinstein is essentially assuming that in addition to the purity of the relationship between a parent and an adopted child, there is an inherent intimidation against doing something unbecoming, whether or not the parent would even desire to do so. This leniency, however, logically only applies when the adoptive parents are living together in a harmonious marriage.