Cut a slice of any type of bread into 1-inch pieces. Let the kids dip each chunk of bread into some water.
Instruct the children to place the bread inside a sealed plastic sandwich bag or in a clear storage container. Close the container and seal it tight with tape.
Place the bread in an out-of-the-way, warm place. The top of the refrigerator or the laundry room are two good choices.
Wear a mask and gloves when you check the bread for mold growth every day, for as long as two weeks. Watch the mold spread and rot the bread. Instruct the kids to record the changes they see each day.
When you are finished with the experiment, throw out the bag or container without opening it.