The 3 toddler books to increase painting skill are:
Finger Painting 101
Handprints of the Masters
Don't Stay Within the Lines
You can also send your high school teen to Art classes after school on Mondays & Thursdays if you missed the books as toddlers.
I gave my kid the Artistic trait and did all that and now as an adult, he paints brilliant or masterpiece paintings all the time. Interestingly the paintings are invariably impressionist style ... either that, or I'm playing without my glasses again...