It's a thing

I thought it might be! I knew I wasn't completely crazy.

http://www.stuff.co.nz/life-style/life/70873407/The-rise-of-multi-parenting-These-five-people-are-about-to-have-a-baby-together

https://verdict.justia.com/2013/10/15/california-allows-children-two-legal-parents