I have a son who just turned 12. His dad and I have basically kept a open-door policy about anything and everything he needs to talk about. Because I am bi, I have always been very open with him about sex and relationships. We have had the sex talk and the puberty talk with him. He turned VERY RED but had some great questions once he realized he wouldn't be ridiculed or sent away for being curious.
With this in mind, we have sheltered him from images or material we feel is too old for him. We still screen all movies, you tube videos, or music he watches at home. We tell him that he is simply not old enough to need to be worrying about adult topics and he should enjoy just being a kid.
About 6 months ago he came to me and told me that if he isn't totally gay he is pretty sure he is at least bi. (wasn't really shocked given his personality) I am just thankful that he knew he could talk to us. I think there is a way to be open and honest while staying developmentally appropriate and I am hoping that is the line I am walking. So far it seems to be working.
He is happy and aware of sex, while not feeling the need to rush things. His friends call him silly cuz he gets embarrassed so easily but I told him that he will be older soon enough and not to rush it.
For me, it was so much weirder talking to him about sex than it seemed to be for him. I think it has more to do with the fact that my family kept a major DADT policy about all things sex and intimacy until after I turned 18 and moved away that I have nothing to reference to. Now I just plan on keeping the conversation open and making a point of talking to him more as he grows into his new sexuality.
PS- He came home and informed me (in a whisper) that he has his first GF today... but can't tell anyone cuz she doesn't want them to get teased by their peers for it. Ahhhhh, Puppy love.... Those were the days.