Water Wow! is a fixture of airport travel for good reason. It solves the specific problem of letting a three-year-old 'paint' without leaving dye on an airplane window or restaurant table.
The activity is coloring by reveal rather than freeform art. Kids stroke clear water across thick white boards to expose full-color scenes, let them dry for ten minutes, and do it again. The boards hold up through dozens of resets, provided your kid doesn't gouge the wet surface with the nib.
It won't replace open sketchpads at home, but as an emergency tool to buy quiet focus in a waiting room or car seat, it consistently does its job.

