Some children socially transition genders by changing their pronouns (and often names, hairstyles, clothing) from those associated with their assigned sex at birth to those associated with their gender identity. We refer to children who have socially transitioned as transgender children. In a prospective sample of children who socially transitioned during childhood (at or before the age of 12; = 6.82), we tested whether the parent-reported internalizing symptoms of transgender children were different before vs. after they socially transitioned. The children were predominantly white (70.6% white) and girls (76.5% transgender girls, 23.5% transgender boys). Their parents tended to have high levels of education (74.5% Bachelor's degree or above) and lived in families with high household incomes (62.7% with household incomes of $75,000 or above). On average, youth showed lower levels of internalizing symptoms after socially transitioning vs. before, suggesting a possible mental health benefit of these transitions.