People often say they do these kinds of things to protect the innocence of children. Those people have obviously never taught children. I used to teach day care (3 year olds) and they knew a lot. We had to watch the playhouse because kids do (or try to do) what they see in their parents' home. Kids are curious. They aren't innocent. They don't always understand everything they see, but they are also often satisfied with simple answers. They are also aware of things like prejudice of all kinds, especially as pertains to them (my niece is bi-racial, and when she was 4 she would ask newcomers if they noticed the difference between her skin tone and hers, and whether they still liked her).

I really doubt kids would freak out over reading a book with two dads or two moms in it, considering all the violence and crap they see on TV. I'm far more worried about the violence and prejudice they see and experience than I am a book that has two men or women kissing and hugging.