Oh that's a neat idea!
I don't have kids but I remember when I was young my mum made up some salt dough and I had fun making things from that, then painting it.http://rainydaymum.co.uk/the-quickest-ever-salt-dough-recipe
Just what a quick search brought up for a recipe.
I remember my mum buying some glass paint, and then going round charity shops finding glass items (vases, ornaments, bottles etc.) and then we would paint onto them. It was that much more exciting because it was glass!
Another thing I remember is making a 'fish tank'. Getting a cardboard box, turning it on its side and cutting off the flaps so its an open box, and then decorating the inside to look like a fish tank. Then you'd make some fish (3D or just paper fish) which you would attach to some fishing wire or string, and stick that to the roof of it so it looks like they're floating around, I can imagine you could also do a similar thing but with birds, or butterflies or something.
Also not quite arty but fun nonetheless- Getting some Plaster of Paris (mod roc) and then making fake casts, so it looks like you've got a broken arm for the day. My Mum did that for me, then I got her to write on the cast too.