Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
In a large bowl, whisk together all the dry cupcake ingredients. In another bowl, whisk together themelted butter, eggs, milk, and vanilla. Fold the wet ingredients intothe dry and mix well by hand.
Fill the muffin cups ¾ full. Spoon about 1 teaspoon of the salted caramel sauce on the top of the batter of each cupcake. With a toothpick, swirl the caramel into the top half of the batter of each cupcake.Bake for 18-20 minutes, or until a toothpick comes out clean from the center.
Remove from the oven and let cool in the pan for 5-10 minutes. Carefully transfer the cupcakes to a cooling rack to finish cooling.
While the cupcakes cool, make the frosting. Using the whisk attachment in a stand mixer, whip the softened butter on medium-high for 4-5 minutes. Reduce the speed to low and add the powdered sugar. Once all the sugar is incorporated, increase the speed to medium-high and add the caramel sauce and vanilla. Whip for 4 minutes, scraping down the bowl, until light and fluffy.
Place the frosting into piping bags or large plastic food storage bags, fitted with a large star tip. Lay the bags on the table along with the cupcake toppings, so the children can pipe icing onto their own cupcakes.I suggest making multiple bags so more than one child can decorate at a time.