After you and your child have had a chance to explore mud in Peep Deep in the Big Muddy, you can do this follow-up activity. Get the mud to the right consistency and make mud pies. Once you both have had fun creating these delicacies, put them in a sunny but out-of-the-way spot to "cook." When some time has passed, check on them to see if they are "ready or not." What happened to the mud? Introduce words like dry, hard, and harden. What happens if you add water back to your mud pies? (You may have to put the mud pies in a bowl and break them up with a stick or spoon in order to shorten the process.) Experiences like these are great for introducing children to concepts of change and cause-and-effect.
Playing With Dry Mud
The Best Mud Pie, by Lin Quinn and Ronnie Rooney.
The Piggy in the Puddle, by Charlotte Pomerantz and James Marshall.