If you plan on decorating a cake with sprinkles (kids love this), make sure you put them on immediately after frosting the cake. If you let the cake sit, the frosting will get a little hard on the outer surface and the sprinkles will not stick, they'll all roll off to the sides of the cake. You need to put the sprinkles on the cake right after it has been frosted so that the sprinkles stick to the frosting.