this is easy to work with and tastes good.

Sorry, I can't find the recipe on this site but here it is: This recipe is really good (I think) because it stiffens up and holds shape REALLY well. Just put it into a bag with a tip and it spreads like a dream. Definitely make sure it is room temperature though. You need: 1 stick unsalted butter (room temperature) 1/4 teaspoon vanilla 1 tablespoon milk 2 cups confectioners sugar Use a blender to beat everything together. If it doesn't come together with just the 1 tablespoon milk, add another and it should come together. I've never tried melting the butter, but that might help also. This refrigerates pretty well but make sure to let it sit out for a while before use, and it absorbs color like you wouldn't believe, just make a few pouches with different colors and your kids will have a blast!

Sorry, that is for them to make fun shapes and small things with, not doing the whole cupcake! :( But here is something that might help, it is a homemade chocolate frosting, and it legitimately (in my humble opinion) tastes like heaven: 2.5 sticks of softened unsalted butter, 1 cup confectioners sugar, 3/4 cup Dutch cocoa (Hershey's and off-brand work just fine), 3/4 cup light corn syrup, 1 teaspoon vanilla extract, 8 ounces any chocolate you like (I prefer semi-sweet) melted. Process the butter, sugar, cocoa, and salt in food processor until smooth. Add corn syrup and vanilla and process until just combined. Add chocolate and pulse until smooth and creamy. You can store this for a while, but again let come to equilibrium temperature with the room :). Hope this helps, my nephew LOVED this stuff

If you want an easy way for them to decorate the cupcakes, you could buy premade frosting in theyre favorite flavors. Take plastic sandwhich bags and place a few spoon fulls of the frosting inside the corner of the bag, then cut a small hole in the corner. They can just squeeze the bag over the cupcakes in whatever shapes they'd like. This is an inexpensive way to do it like the professional frosting bags they sell.