Cut cantaloupe in half. Your child can help scoop out the seeds with a large spoon. Slice each half into many thin wedges (sideways these should resemble crescent moons). Your child can remove the peel of each cantaloupe wedge with a plastic knife. Put in large serving bowl.
Demonstrate for your child how to make a watermelon ball using the melon ball tool. Your child can try his or her hand at making melon balls. Add all to the cantaloupe.
Cut the casaba or honeydew melon in half; remove the seeds with a large spoon. Make melon balls and then cut each ball in half with a plastic knife; add to other melon.
Mix the melon in the bowl. Talk about how you have three moon shapes in the salad: a crescent moon (the cantaloupe), a half moon (the casaba or honeydew melon), and a full moon (the watermelon).