I don't have kids yet, but I'm not going to get too into sexual stuff before they start asking questions. When they ask, I'm going to explain "Either, both, or neither" as far as sexuality goes. I'll explain gender variances as they get a bit older.
As is, one of my closest friends is a very open lesbian, many of my friends are bisexual, and at least one friend is trans. I don't think it'll harm the kids to meet Uncle Colin just because he was born Aunt Colleen, or meet Aunt Lily and her partner June.
I don't believe in forcing things down kids throats, but letting them observe the world with a light, guiding hand.