What a great gift idea!!
You could get them custom artists aprons... canvas apron with their name embroidered on it. You could also get them various sizes of art canvas (you can get them as small as 2x2 inches) and some acrylic paints (Liquitex Basics is a good brand to start with, and are pretty reasonably priced). Also, for the supplies you could use gallon and quart sized paint cans from the hardware store, or you could use buckets. The Land of Nod has some really cute
buckets, and they come in
pastel colors as well.