Early finishers help clean, sort, or sweep the floors. Sometimes I hand out
modeling clay to reward those who are on task. Sometimes I put a cap on the
lesson by having them sit on the floor in line while I read a short book that
goes with the topic, while some are collecting crayon buckets, paints, brushes
or water containers.
Life is exciting when you come to art. I always surprise them with something
new. Sometimes I give them a piece of colored chalk to take home, because of
their good answers during the lesson.
Remember the young and tender age that you're dealing with, you want them to
still enjoy art by the time they get to fifth grade. If you can keep the
structure the same, constant rewards and varied lessons, you might keep them
interested by the end of elementary school.
Lots of Luck
I taught pre-K for a year before I taught art, so I know what you're thinking
as you teach them.