Fizzy Bath Bombs for all ages.

½ Cup Epsom salts
½ Cup baking soda
¼ Cup cornstarch
¼ Cup citric or ascorbic acid (found in beer making stores)
Mix very well.
Add up to ¼ Cup olive oil, until the consistency of pastry dough.
(JUST until it starts to stick together)
Add a few drops scented oil/liquid tempera if you want them scented/colored.
Form into small, golf-ball sized balls. Store in cellophane wrappers.
You may press mixture into small multi-cavity mold. Allow to dry. Store in an airtight container.
(You may add colorant if you do not mix in any water. Just blend into the olive oil before mixing.) ADD NO WATER!           
                   Add one or 2 bombs to a tub of water. This is a fun project that will especially be of interest to young children. However bath bombs are soothing and relaxing for adults too. Select an essential oil scent that will appeal to the age and gender of the person who will use them. Young children using bath bombs should be supervised. For external use only. 
                 Toss one or 2 in the tub and watch them fizz and enjoy the Ahhhs....and giggles. :)