Pour an even coating of sprinkles in the bottom of each heart mold. If desired put a single M&M in the middle of the sprinkles with the M side facing up. Melt the white chocolate in the microwave by putting chips in a microwave safe bowl and microwaving for 30 seconds. Stir the chocolate. Microwave an additional 15 seconds. Stir. Repeat until chocolate is just melted and smooth. Stir in coconut oil, one teaspoon at a time until the chocolate slides easily off the spoon and is shiny. Spoon into the molds, covering the sprinkles. Tap the mold in between to encourage the chocolate to settle evenly.
Repeat the whole process with the milk or semisweet chocolate. Go slowly when adding the coconut oil. The milk or semisweet chocolate will likely need less coconut oil than the white chocolate to achieve the same shine and slip. Spoon the melted chocolate on top of the white chocolate layer. Jiggle to encourage it to evenly settle.
Let mold set in the fridge for about an hour. Pop the candy out of the mold and enjoy.