I often use “Athens® Mini Fillo Shells” for quick desserts; the shell packaging is a plastic container with small wells. Having a feeling the containers would be useful I saved them…ta-da, one use for them is a kid friendly paint pallet! I pour a little paint into each of the wells, let my little artist go to town, when he’s finished I rinse the container and stick back in the paint basket. Sorry for the pour image quality, I had to use my camera phone.
FYI- Crayola smocks are great; inexpensive and washable.