Panacea it will hurt them. They can start thinking that two kissing men or women is OK.
You can't say for sure it will hurt them, first off. I'm guessing you're not a child psychologist/pediatrician. That's simply your opinion, but fact it is not.
In terms of thinking homosexuality is ok, I suppose most people believe it is ok already, so it isn't as if having a new generation of kids think the same thing as the old generation in regards to homosexuality is that shocking.
But you didn't answer my question fully...given what you've said, what specifically about thinking homosexuality is ok is harmful?