My girl's man has two adorable kids, and a third he see's once every two weeks, the whole divorce visitation thing.
The three sweethearts have easily taken my girl on as a parent, and just a few weeks ago she was referred to as 'second mummy', which is of course painfully cute.
You cannot hide facts from children forever. Pain now, or pain later, if there is going to be pain it cannot be avoided. It's best to simply answer the questions as they come, lies don't get you anywhere!
In my opinion, being the kid in school with the poly parents isn't so bad. I doubt it would really come up. There are so many things 'worse' that a kid can be picked out on. Then again, I've yet to have a child in school, or be that child, so this is me guessing.
I have many in my family. And this is good.
I have many friends. And this is good.
I have many teachers. And this is good.
I have many loves. And this is a great concern. The greatest insanities of this world are those stock full in the face of all.