All you need is:
~ white washable paint
~ black card stock paper
~ markers (for eyes, nose, mouth, buttons and any other decorations - we did a scarf also)
We put the paint on the bottoms of their feet and then they stamped their footprint on the black card stock. Make sure you put the toes down at the bottom of the page as they will the base of the snowman/fallen snow. The heel part is the head of the snowman. Then I just let them use their fingers to put snowflakes all around the paper.
After they were completely dry, we decorated them using different colored sharpies. They're absolutely adorable and a great way to remember what their tiny little feet looked like! :)
(The top is Jacob's and the bottom is Henry's.)