Washable markers as face paint
I see you’ve got a hack about washable markers acting as nail polish, but they make great face and body paint as well. Our 3-year-old daughter goes through these phases where she wants to be a certain animal for a few days at a time. We draw a face on her (or even better—she draws it on herself), and it comes right off in the tub. Sometimes she goes completely Burning Man on us and draws all over her entire body. It’s fun and creative for her, and fairly harmless. Word of warning: it comes right off on bedding too, so wash it off before you put them down for sleep. We also won’t let her on the couch when she’s gone into body painting mode.