Kyle,
It would take years to improve their motor skills. If it is OK for the wood to show, try this:
1. V Carve the design
2. Use a couple of coats of sanding sealer on the top including the v carved recesses
3. "Slop" on the paint in the v carved recesses. Make sure it covers all of the V recess. Accidental paint on the top surface is OK. Wait for paint to dry completely.
4. Sand only the top until the slop is gone
Result - a perfect paint job!
Paul Z