Make frosting: beat butter until creamy using a hand or a stand mixer. Slowly mix in powdered sugar, 1 cup at a time. Add salt and vanilla, then add 2 tablespoons of heavy whipping cream. Beat at medium high speed until smooth, adding more cream as needed for desired consistency.
Divide the frosting into 3 bowls. Color each a different color: pink, blue, purple.
Reynolds Kitchens Plastic Wrap Hack: lay out a piece of plastic wrap. Place one color frosting in the center and roll up like a log, squeezing the air out. Twist the ends to seal. Repeat with remaining colors of frosting. Cut of one tip of each plastic frosting log. Place all three, cut side first, into a large plastic pastry bag fitted with a 1M tip (or other desired tip).
Prepare the cupcakes: cut a small hole in the center of the cupcake and remove the piece of cupcake. Fill the hole with sprinkles, then replace the bit of cupcake.
Frost cupcakes with the swirl frosting. Top with additional sprinkles, if desired.
Store in an airtight container in refrigerator for up to 4 days.