Ok, this is a product found at the craft store which I think is great for toddlers just starting to experiment with making art.
They're called Bingo Bottles or Dot Art bottles, and what they are is a squeezable bottle with a sponge top, filled with non toxic washable watercolor type paint. At I think $4.99 per bottle, they aren't cheap but judging by the amount of paint used each time I'd say they'll last quite a while. Bean has really taken to these since we got them, as they're so easy for her to use, all she need do is grab hold and press (or bang!) the bottle onto the paper - simple and fun! I often set these out before bedtime in the evening as a less messy alternative to painting...
But often it becomes a mixed media piece! ;-)