If you ever make Pillsbury cinnamon rolls, you are familiar with their little icing containers. These things are great. We use them for holding our water when we paint with watercolors, I use them for Landon's small portions of baby cereal he is now eating, and most recently, we used one to make a stamp.
Ink (or paint), an icing container, and self adhesive foam stickers are all you need. Because Ava's name and individual letters in her name are all symmetrical, we were able to make a stamp of her name out of foam letter stickers. It was easy for her to tell if she had the letters on the ink pad and where she was placing the stamp on the paper because of the partial transparency of the icing container.