"Save Fred." Group students in fours. Pass out one paper clip to each student. Put a gummy ring on a desk. Place a clear cup upside down over the ring. Put Fred, a gummy worm, on top of the cup. Tell them the boat (cup) has capsized, and they need to put the life preserver (ring) on Fred before he drowns using their paper clips, no touching with hands!
STEM idea: One of the most popular challenges is the Spaghetti Tower (sometimes called Marshmallow Tower) challenge. It's actually a completely doable, fun way for your kids to experiment, collaborate, and problem solve.