@Quaagars
Most of these evil religious parents aren’t going out of their way to introduce the concept of same-sex relationships to their young children so I really think you are overestimating the negative messages young Tommy is getting
Who said they're evil?
No-one apart from yourself.
You're missing the point, yes we know that the parents aren't going out of the way to introduce the concept of same sex relationships.
Heterosexual relationships are default "the norm" and so that's what people see if that's what they've only ever known.
Why is it wrong for children to know it's OK to be gay too?
Well it's not really the question, is it?
The implication, explicitly, is that it is ok for the state to choose sides on issues where there is not a heterogenous opinion, and teach it to children whose parents think differently. If, for example, the dominant view was that same sex marriage was not a good thing, the school could teach that view and parents who disagreed would just have to suck it up.
It's possible to teach small kids that it's not their place to criticise, make fun of, or make rude comments about other people's families, which is entirely true and applicable in pretty much 100% of school circumstances.