Line a large baking sheet with parchment paper and set aside
Melt both milk-chocolate and dark-chocolate chips in separate bowls in the microwave in 30-second intervals, stirring well between each interval, until completely smooth.
Pour the milk chocolate onto the parchment paper and use a spatula to smooth it into an even layer. Add dollops of the dark chocolate on top of the milk chocolate and use a toothpick to swirl the two together. Place gummy bears on the chocolate
Place in the fridge to allow the chocolate to set, about 15 minutes.
Melt the white chocolate in a Ziploc bag in the microwave (also in 30-second intervals), snip the corner to make it into a decorating bag and drizzle the white chocolate on top of the bark. Add sprinkles and decorate as you wish.
Return the bark to the fridge for another 15 minutes to set.
Transfer bark to a cutting board and cut up bark into desired pieces. Store in an airtight container at room temperature until ready to serve.