Fruit Dip (approximately equal portions cream cheese and Marshmallow Creme mixed together)
Or any any other combination of stackable, spreadable, sprinkleable foods you happen to have on hand
In general, my kids like to eat, but we don't often have the kind of snacks they can actively participate in creating. This was a treat for them and easy for me (versus really cooking or baking something with them).
I spread the peanut butter and dip onto several crackers, filled small bowls with toppings, then let the kids build their own little masterpieces. Pretty good!