raised salt painting: create design with glue, cover glue with table salt. Touch watercolor brush on salt, without smearing and watch color be absorbed by salt. Let dry. This looks fantastic. So, inverted rock salt painting.
Bottle maze: clean out an empty juice bottle, draw a maze along the outside with letters placed about every inch; place a magnet inside the bottle and one on the outside to hold and trace. Great for bilateral coordination and crossing midline.
Magic Milk Paint idea from Modern Parents Messy Kids. This is another one of those awesome 'science meets art' activities for children, and you only need milk, dishwash and food colouring to do it. Looks fun :)