get a batch of baby chicks. hours of fun and mostly harmless.
gold fish in a kiddie pool are also great. you can move pool to wherever you need to work.
my little guy has had his own marked off patch of garden every year since he was two. ( bigger every year) He does whatever he wants in there. He can plant it with seeds one day, bulldozer and excavator the next and flood it after that. stuff still comes up and he has a ball. ( hours of me getting stuff done) I get to have solid boundaries and rules in my garden and he has complete freedom to play in his.
Growing trays of micro greens is a great way to get kids to eat greens. I turn the kids out in the green house first thing in the morning to graze the flats of micro greens. They are warm so they are happy to be outside and I can get all my zone one chores done and can keep an eye on them.