Pour baking soda, corn starch and epsom salt into a mixing bowl. Stir until combined.
Add drops of food coloring and fragrance oil. I started with 6 drops of red and 4 drops of purple and 10 drops of fragrance oil. Get in there with your hands (rubber gloves will keep your hands from getting the food coloring on your skin). Mix, adding more food coloring as needed until you get to your desired color. (Note: when you add the coconut oil the color will darken some.)
Add the citric acid to the bowl and stir until combined.
Slowly add coconut oil to your mixture one tablespoon at a time, stirring with a spoon to start and then mixing with your hands until the mixture holds together like wet sand when packed together.
Add sprinkles and candy to the bottom of your silicone molds.
Divide your bath bomb mixture between the cavities of your silicone mold. Press the mixture firmly into the mold. Your bath bomb mixture should be packed down firmly.
Add more candy sprinkles to the top of your bath bombs. Press firmly so the candies are embedded in the bath bombs. If you are worried about the candies sticking on top you can pour a bit of coconut oil on top and press down with a spoon to seal them in.
Leave overnight to dry.
Once they have dried for 12 hours or more, carefully remove from the silicone mold!