Who doesn’t like mud!?! I sometimes chat about how you make mud and whether soil has clay, or sand or plant matter in it. As soon as the children have started to stir the soil/water I go around and ask to see their hands. They proudly show clean hands and I tell them off for being too clean and smear mud over their hands. I can still hear the cries of shock and sometimes horror (I will be sensitive to the children, I have seen a child shaking and retching (but this was an extreme reaction) because of concern about getting dirty). Once the children have relaxed into the play its fun to point to a clean arm and helpfully inform the child they have a mark on their arm and then make one with a muddy finger.
Post mud making we make mud faces on trees and mud monsters with pinecones, its a shame to waste good mud.