All you need is...
~Chalk (we use something like this)
~Dark heavy paper (we like black construction paper)
~Aerosol hairspray (I keep some on hand just for chalk art)
Once your child is satisfied with their creation, spray the entire image with hairspray (keeps the chalk from smearing). We've found that pinning the drawing tightly to the walls keeps the paper from curling while it dries.
I really do love the results. So do they. And it really is so very simple. Which then leads us to my eternal conundrum... What do you do with all the resulting piles of beautiful art?