Off the top of my head, I can think of 10 families I know/have known--as a parent, and I've been a parent for 25 years--where the parents were same-sex couples. Never once on the playground, classroom, PTA meeting, or pediatrician's office was this an issue that was too confusing for my kids, the kids of the same sex couples, or any other kids they played with/went to class with. For little ones, an effort was made to have a couple of picture books/early readers featuring children with same sex parents, same as efforts were made to have picture books/early readers with children who were black, latino, asian, etc.

There are many ways to configure a family, and in my experience, children understand this--without any pesky confusion or assumptions re sophistication.