Son keeps asking why he has two houses

My 5yo asked me yesterday "Why do I have a bedroom at your house AND a bedroom at mommy's house? Other kids don't."

I froze. How do you explain co-parenting to a kindergartner without making them feel like something's wrong? I just said something about how both mommy and daddy love him so much we both want to spend lots of time with him, but I could tell he wasn't really satisfied.

Anyone have scripts that worked with young kids?