A quick and simple art activity to do with kids from age 3+ is to cut and paste collages using your junk mail. A great rainy day activity which you can easy theme scenes. Use safety scissors for younger ones, this will help get them use to the cutting action and how the hand needs to move helping the fine motor development and use coloured glue so they become aware of where the glue ends up.
In this example I have used a jewellery catalogue and cut out shapes for Missy. Look for love hearts pendents, tree pendents, snakes bracelets, dragonfly pendents, earrings, rings, and so on.
Get the local grocery catalogue and get the kids to create fruit and vege hampers. Or theme it to suit their interests. Make a toy shop from toy catalogues and so on.
Reuse old their old and abundent paintings as backgrounds.