My entre into this space is through neuroscience (animal play, what it's for, how it works) for which the work of Jaak Panksepp is canonical. In humans, I've read some of Peter Gray's work -- here's a TED talk that looks like a reasonable orientation.

You know, this is a reach, but one of the most life-changing books I've ever read is on improv. Strikes me that it could be a really good thing for where you are in your life, for yourself and your kids. It's a serious read, FYI, but I don't use the phrase 'life-changing' lightly.