We sometimes have "snowball fights" with crumpled up paper, he thinks it's hilarious! And there's nothing better than a good old-fashioned dance party to lighten the mood. And this is rather obvious, but I taught him various old-school exercises (arm circles, jumping jacks, bicycle kicks, windmills, etc) and he likes calling out what exercise to do next. I get my work out too. ;) I think he likes that he gets to run the show more than anything else.
We have a deck of cards called Yoga Pretzels that are fun too, each card is a different yoga pose or activity. It doesn't matter if they do it right, per se, it's just fun to do.
Follow Mothering