Here is a cute, easy idea for making a heart pocket using 3 paper plates. They show the paper plates being painted (pretty messy for that many kids, lol) but you could let them decorate the plates with crayons, stickers, or punched out hearts.
I have grandkids the age you're talking about, and some can have a limited attention span at that age. I would be sure whatever you do to keep it simple, and do some things ahead.
i.e. for this particular project, the paper plates are folded in half. You could do that part before you pass them out to the kiddos.
Paper Plate Heart Pocket - Free Arts and Crafts for Kids