The Biblical Archaeology Society's Bible History Daily has an interesting slide show here on how to make mud brick. This might be a project to consider when teaching Exodus 5:6-21.
The link above also includes the following instructions.
Their efforts produced great results, and although time-consuming, their procedures can be followed to create mudbricks of your own:
1. Mix topsoil and water to create a thick mud.
2. Add straw. While the composition of the mud will affect the exact proportions, as a general rule, add a half pound of straw for every cubic foot of mud mixture. If you have access to grain chaff (a byproduct of threshing), you can use that as temper. If not, chop straw into very small pieces—called straw chaff—and use that.
3. Knead the mud mixture with your bare feet for four days.
4. Once it has fermented (after four days of kneading), leave the mixture alone for a few days.
5. Knead the mixture again on the day you plan to form your mudbricks.
6. Pour the mud mixture into molds (the shape of your choosing) and let them solidify in the molds for at least 20 minutes.
7. Remove from molds and deposit on a drying floor layered with sand and straw to prevent the bricks from sticking to the floor itself.
8. Let the bricks dry for a week. After the bricks have dried, they are ready to be used—whether to build something new or to reconstruct ancient walls!