When J received some Amazon money from one of his grandpas I knew I wanted to buy some art supplies. I bought him some Crayola Washable Kids Paint set of 10 Bottles (2 fl oz/59mL) because I knew he would get messy with it!
When it arrived we did a couple different activities with it- paintbrush free! I used the box that his laminator (from the same Amazon order) came in to put the paper in. (Yes, I said HIS laminator because I'll mostly be using it to laminate things for our "homeschool").
I taped down a sheet of paper, let him choose 3 paint colors and squirted a bit of each color on the paper. I put in a bouncy ball and a plastic golf ball for him to roll around. He was frustrated at first because he didn't know what he was supposed to do and was more interested in pouring the paint into the box (I was NOT going to let him do that because I knew he would want to dump the whole thing in). Once I showed him what to do he enjoyed rolling the balls around to make a design.