wouldn't this be cute to tape the grandkids names on the canvas and let them do the fingerpainting to make their own sign for their room. Tape word on canvas - finger paint - remove tape. Must do this!
Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.