Sex education for your child

So a few months ago my son confided in me that his friends talk to him about boobs, and they talk about squeezing them. My recourse to this was I know your curious because girls have different parts then boys but it's inappropriate to touch anyone else's body and their private parts. Well that led to him asking about babies and sex. I've made it very clear that he can ask me anything. I'd rather him learn the truth through someone he can trust. Being I work in the medical field I keep all of our talks as anitomically correct as possible so he takes it seriously and understands it's not a game. Well I told him that it takes a mommy and a daddy to have a baby. That they have to have sex which gives the sperm the boy makes to the girl for her egg and when they come together it makes a baby. Then it stays in the mommies tummy till its big enough to come out. Then it comes out a special hole just for babies and it's behind the girls pee hole. He was like it's that close to her butt and I told him yes. And he was good with that and hasn't really asked anymore questions, well except if me n my SO are gonna have a baby so he can be a big brother. Anywho today I came home and the sitter informed me she thinks she saw him "riding" the arm of the couch. I think he may have discovered that it can feel good to touch down there. So now I'm at a loss as to how to have this talk with him. Have you talked to ur son? Do yall have rules? How old was ur son? I know this isn't everyone's style and that's okay I'm looking for helpful and insightful information only. Thanks