This casting project may take a day or two to complete, but the end product -- a pretty holder for jewelry, coins or other collectibles -- will make a lasting impression on whomever your child bestows it.
First, prepare the mold by trimming the sides of the carton or tub so that they are about 2 1/2 to 3 inches tall.
Next, partially insert the kabob sticks into the center of the object you plan to cast, evenly spacing them around the circumference (with hard objects, you may have to hammer starter holes with a small nail). Rub Vaseline on the portion of the apple or squash that will be submerged in plaster (skip this step if you're using a baseball). Then rest the skewers on the sides of the mold.
Use the bucket and stirrer to mix the plaster according to the package directions. Slowly pour the mixture between the object and the carton walls until one third of the object is submerged (no more, or the object will be hard to remove later). Gently tap the mold on a table to release air bubbles.
After one hour, lift the object from the plaster. Carefully remove the mold and let the casting cure completely (about 24 hours). Then prime the plaster with shellac or spray matte, let it dry and the casting is ready to paint. For the best effect, use a contrasting color to accent the hollowed portion. Or sponge a darker hue on the top and sides once the base coat dries.