I would have overworked it for sure. It is interesting to sit back and resist interfering and see their little minds create. I try to let my kids do their own work, even if I show them how to draw something it's usually on a different piece of paper so they can copy the technique.
This is much more minimal than I would have done, I was inclined to put full profiles on the side, but the faces work well, and splinter on the back is cool. A true Ninja not seen.

Yup true ninja :D. I think thats really great he got to do it.