Unless the homosexual couple in question aren't humans, then I'm afraid you are mistaken. Just like a straight or religious parent will "teach you to hate" homosexuals and listening to Paradise Lost, a homosexual couple can similarly teach you to hate the majority of straight situations or discriminate more than they should against religion. The "special" condition of their marriage doesn't make them any less faulty than all humans are. Each side has things they follow, and similarly has things they are against. And through that, gay or straight, you will see hatred being taught.
The real problem for a child raised by a homosexual couple isn't what they'll be taught by their parents, that's more or less similar. You could argue that by having two men or two women as parents might affect the broadness of ideas you'll get in contact with, but I don't know about that. The real problem is the treatment of the children in question by their immediate environment. As many have said, making marriage between homosexuals legal isn't gonna make the discrimination of some disappear overnight. It's still a world where you may choose to insult someone by calling them gay. So what will the child face from its surroundings, about what his parents are and what he will become?
I mean if the children were raised in complete solitude then it would be a problem because they are missing development but you seem to forget children learn a lot from interacting from the world and if they learn good things and are more or less raised in a good environment, then they have it good. I can't argue that children raised might have issues of broadness because literally most problems the world had came from heterosexual parents. It is true that same sex parents can raised their children with hate (they are human too) but that is just like seeing an Atheist pray to God. Its just something I've never seen from my interactions with the LGBT community. They were completely loving and fun to be around even though they know the hate against them. This hate comes from religion, which was taught to children by heterosexual couples.