I saw this while doing some research on some fun things to do. I actually had another idea but I'll post that for next week. ;)
My youngest, A, loves to paint. I thought, "What a great way to spend a Friday!"
Gather up any large piece of material you can find - cardboard, butcher paper, fabric - and paints. You might want to make sure they are water based so they clean up easy! Wear old clothes or a paint smock and then just let them go to town!
In my experience this is best done outdoors!
If being outdoors is not an option you could do a smaller version of this inside. Just spread out a bunch of newspaper on the kitchen floor or an old table (we use an old folding table that we set up in the kitchen). As long as she is not flinging the paint across the room I let her have free reign for artistic expression.
It's fun to see what they'll come up with!