I have found when I do painting with my 2 year old, that see gets more bore easier when she is just painting on paper. So I started drawing images with a thick texta on the paper, then she has a focus - 'to colour in between the lines'. So still has a short attention spand, but she is more engaged this way.
Here are some examples. (Ps Who cares if you can't draw, they can't either, so look for some colouring pages then).