So my first attempt at these failed horribly. The baking soda clay hands were a very nice white, but dried and cracked. So it's back to salt dough.
2 cups of Flour
1/2 cup of Salt
1/2 cup or less of Water
Start by mixing all the ingredients together. When you have a nice playdough type clay roll it out onto a floured surface and push your childs hand into it. (TIP: You could just trace your childs hand on paper and use it as a template for the dough- but you will not get the indents that way). After that cut out around the hand carefully and play on a cookie sheet lined with parchment paper.