Cut a Stencil out of Department Store Clothes Boxes
I was searching for card stock at home today and was having trouble finding anything sufficent. I was digging through my walk in closet and found clothes boxes.  Like the ones JCPennys wraps clothes in at Christmas time. Ha, so anyway I created some sick stencils just using that. If you unhinge the corners and flip em up they act as a cool "tray" and catches unwanted paint from transfering.... I don't know if that really helps but it's one of those items lying around the house that kids could easily access.