I was thinking about this the other week. It's only tangentially related, but I've heard that children being brought up inside poly households (the kind where there are multiple guys and multiple girls all sexually involved with some combination of each other) are starting to show up as having certain risk factors.
Apparently the unspoken relationship dynamics of a sexually fluid household tend to get a bit strained, and children - who instinctively pick up on such things as part of their drive to seek and maintain nurture - end up affected by it. It's way beyond a developing child's ability to comprehend adult emotional and sexual dynamics, and so not only can the child end up with confused parental imprinting, they also end up competing with unrelated adults for their caregiver's attention and affection without realizing it. Also, the partner count and soft periphery that such households often have brings with them the same risks associated with children whose parent repartners (e.g. single mother with series of boyfriends).
I've not studied the topic myself, but I thought this was interesting to consider against the kind of polygynous households discussed ITT, which if nothing else at least have one father to unify beneath, a more limited set of emotional/sexual dynamics, and something of a social framework setting their expectations.