Why is it relevant in a kid's show?
Get your mind out of the gutter.
I just fail to see why you need to make a pony a lesbian in a kids show.
Why bring that up at all?
So that it reflects the real world, perhaps? Same reason shows have families with moms and dads in them.
Are the heterosexual couples going to tell the kids about the sex they're having?
Many kids shows I enjoyed never had any couples or parents in them, which avoids that altogether.