1. Take a three yr old, a canvas of any size, a roll of masking tape and some paints.
2. Cut lengths of tape and stick in random places on the canvas.
3. Paint the shapes in various colours.
4. Allow to dry and remove the tape.
This is not an original idea. I saw it on another mums blog awhile back, but I'm sorry to say I can't remember which blog it was.
Considering MJ has the concentration span of a flea this was a successful activity. He didn't complete it all by himself but he did start each stage before getting distracted and kept coming back to it.