Grab a medium sauce pot and fill it halfway with water. Grab a heat-safe bowl and place it over the pot. Make sure the water is not touching the bottom of the bowl.
Pour in chocolate chips and turn heat to low. Mix continuously until everything is melted.
Add a spoonful of melted chocolate into one mold cup. Use the spoon or a pastry brush to make sure the entire mold is covered with chocolate. Make sure that you have covered every part of the mold with the melted chocolate. Repeat this process for each individual chocolate mold, then place in freezer for 15 minutes so the chocolate can set. Remove the molds from the freezer, then remove the chocolate from the molds. To do this, gently press the silicone to turn inside out to slowly push the mold.Place three of the molds seam-side down on a parchment lined cookie sheet and set aside.Turn the other three face up onto another surface and fill them with about 2 tablespoons of hot cocoa mix and a small handful of mini marshmallows. Grab the three molds on the cookie sheet and place the tray over the warmed double boiler set up for about 10-15 seconds. You want the seams of each chocolate shell to be slightly soft but be careful not to over-melt them.Cover each cocoa-filled chocolate half with an empty half to seal it.
Decorate your hot chocolate bombs with melted white chocolate, sprinkles, or anything else you want.
To make your hot chocolate, add one bomb to a large mug, then pour hot milk over the bomb. Watch the hot chocolate bomb melt. Stir and enjoy.