This article is all the rage among my Facebook friends. Sounds interesting! If only I had time to read.
Although research indicates that single parenting is not by itself worse for children than their being brought up by both their parents, there are reasons why it is better for children to have more than one committed parent. If having two committed parents is better, everything else being equal, than having just one, I argue that it might be even better for children to have three committed parents. There might, in addition, be further reasons why allowing triparenting would benefit children and adults, at least in some cases. Whether or not triparenting is on the whole preferable to bi- or monoparenting, it does have certain advantages (as well as shortcomings) which, at the very least, warrant its inclusion in debates over the sorts of family structures we should allow in our societies, and how many people should be accepted in them. This paper has the modest aim of scratching the surface of this wider topic by challenging the necessity of the max-two-parents framework.
Feminist Philosophers 
I’d be curious to read the article. I wonder whether the concept of tri-parenting or multi-parenting more generally differs from the concept of allo-parenting, as elaborated for example by Sarah Hrdy. Hrdy has completely convinced me that 2 is not enough when it comes to parenting, given that child-rearing in humans is so demanding, and that the solution is allo-parenting.
Grandparents included, many children have a whole lot of “parents” already in many families.
I grew up in the South surrounded by extended family, and my aunts and uncles had second-parent status.
I grew up with divorced parents, both remarried. So that’s four parents. I get along with them all, and they all get along with each other. I switched every day: Mondays and Wednesdays at my mom’s, Tuesdays and Thursdays at my dad’s. For a while weekends were split, too (Saturday at one, Sunday at the other), but then we alternated those.
I always thought it worked just fine. I honestly didn’t realize there was a max-two-parents framework until just now.
Sorry, that anonymous is me. (I wasn’t sure which cross-domain requests I needed to allow to enter a name.)