Place red candy melts in a microwave safe bowl and heat at 30 second intervals. Stir the chips between each interval, until the chocolate has melted completely. Optional: use a candy melter to melt the chocolate.
Once the red chocolate has melted completely, arrange the silicone molds on your workspace.
Spread a spoonful of melted chocolate inside one cup on the silicone mold and use the back of the spoon to spread the chocolate up the sides of the mold. Continue this process until all of the molds are coated with chocolate. Tip: the thicker you can get the chocolate around the rim of each cavity, the sturdier it will be and the easier it will be to seal the two halves together. You can always add another round of chocolate to the sides if they seem too thin.
Set the remaining red chocolate aside for sealing and decorating the bombs.
Allow the chocolate in the molds to set and harden completely (approximately 2-3 hours). This process can be sped up by placing the mold in the refrigerator.
Once the chocolate has set, remove each chocolate piece from the mold and lay half of the pieces on your work surface to be filled.
Add some instant hot chocolate to half of the pieces (approx 1-2 TBSP to each half).
Add some marshmallows, candies, and sprinkles to the pieces.
Reheat the red chocolate at 15 second intervals until melted. (Or in the melter if that's what you originally used.)
Pick up an empty chocolate piece and dip the edges into the melted chocolate. Carefully place it on top of a filled piece and press lightly into place. Use your finger to smooth the melted chocolate around the seam. Continue until all of the chocolate bombs are sealed.
Melt the pink chocolate according to the directions on the package.
Place chocolate into piping bags and drizzle each color over each bomb.
Sprinkle remaining sprinkles over the top of the bombs (quickly, before the pink chocolate hardens).
Allow the hot chocolate bombs to set before using (about an hour).
TO ENJOY THE HOT CHOCOLATE BOMBS: Place a bomb in the bottom of a mug. Pour one cup of hot milk over the top of the bomb to melt the chocolate. Once the chocolate has melted completely, stir all of the mug's contents to combine. Enjoy!