That seems a little bit of a biased way of thinking about it, don't you think?
If kids are taught how straight sex and marriage works, then why can't they be taught how other relationships work? I mean, there are gay kids who were taught about straight relationships only, and it, for the most part, didn't mess them up. Why are we all of the sudden worried about something we have doing to kids forever? When has discussing straight relationships with kids ever been an issue? It hasn't. Let's not treat others differently.
We have always said to boys "do you have a girlfriend?" and vice versa and always push that down kids throats. We always assume as soon as kid likes the opposite sex that they are boyfriend and girlfriend, even as a joke.
If we really gave a shit about "protecting innocent kids", we would stop pushing that heteronormative garbage of dating and sex and relationships down kids who don't even understand what sexual arousal is.