I used to belong to an Early Childhood PTA group when my daughter was very young and one of the speakers we had was a child psychologist. I don't remember her exact specialty but I do remember there was a lot of talk and questions about how to deal with kids and their curiosity about their and other people's bodies. One of the parents asked about when to stop bathing with the kids during this session. The speaker recommended transitioning them to bathing by themselves by the age of 6. I can't remember her exact response but it had something to do with that's when it's more than just curiousness about the appearance of differences in our bodies and it becomes more cognitive for them. She also said that kids talk more about their experiences at home with other people outside of the home at that age too so something very innocent could be misconstrued as something sordid depending on who they were talking to and what they said.
Like mentioned by other moms, she also talked about being honest but not overly descriptive when children ask questions, to use proper names for body parts and teaching kids about parts of their, and other's, bodies no one else should touch.
It was a very informative session and she was one of the most popular speakers I believe.