I don't know if you remember Dogster, who was a very active member but has disappeared lately, she taught her dog to paint and there should be a thread around somewhere. From memory it would be in Off Topic Forum and I think, not sure, about six/eight months ago possibly more.
From what I can recall, she used ordinary non-toxic children's paints and just ordinary brushes. I was going to teach Rakins to paint, but well that didn't quite happen, but I'll start teaching Leaf as soon as the weather's cool enough to work outside.
Running a bit late at present, but will try later to find the thread for you.