What you will need:
A canvas: any size you want! (But the larger you get the more "work" your little one will have, so if they get distracted quickly, I would use a smaller canvas)
Finger paint (or any paint you are comfortable letting your little one use)
painters tape (after actually doing the craft, I would recommend the skinniest one you can find!)
Make your design with tape (you may want to do this ahead of time, it can take awhile getting it just right and your little one might get antsy!)
Make sure to push down on the tape pretty good to avoid letting the paint bleed under the tape.
Let them paint! Either using a paint brush....
or your hands!!
Make sure its COVERED in paint and then let it dry. Peel the tape and you have your masterpiece!