Wash the watermelon well and dry it. Slice off roughly the top one-eighth of the melon. You do not need to measure it, just make sure you create a straight, flat opening wide enough to get a spoon inside.
Use a large spoon to scoop out all the red flesh. Unlike a pumpkin, this is the fun part, so sneak a bite while you work. Drop the scooped watermelon into a bowl and save it for the fruit pile.
Flip the watermelon over so it stands on the flat cut side. Draw eyes, a nose, and a mouth with a marker, then cut them out with a small paring knife. I placed the mouth low on the front so the fruit could tumble out easily.
Set the carved watermelon toward the back of your platter. Leave a big open space in front of it. That empty space is where your "spill" of fruit will go, so give yourself plenty of room.
Cut the scooped watermelon, the cantaloupe, and the bananas into bite-sized squares. Remove the green tops from the strawberries and leave them whole. Soft fruits like cantaloupe and banana are easy for little hands to cut, so let the kids help.
Heap the cut fruit right in front of the open mouth, letting some pieces fall out of it. Mix the colors so the red, orange, yellow, and pale green all show. Serve right away and watch everyone laugh.