I have always painted with my babies, my oldest daughter seemed most content to just watch, she liked it, and she never interfered when she was a baby, she never even reached for my brush. It worked really well, as you can see here and here and here.
My second was almost as easy to paint with as you can see here, here, here, here or my favorite, here. She did start grabbing my brush, and things got a little messy a couple of times.
This little one is proving to be much more active during our painting sessions. I still love it. I treasure it. It makes me happy.