Decorate cupcakes. Using light blue icing, spatula ice all the cupcakes.
Prepare four decorating bags with couplers. Fill separately with medium blue, brown, red, and white buttercream.
Cloud Cupcakes: Attach tip 10 to white bag; pipe fluffy swirls on cupcake to create cloud.
Airplane Cupcakes: Attach tip 10 to white bag; pipe a long bead for the body of the plane. Switch to tip 6; pipe wings and tail. Attach tip 1 to red bag; pipe line details. Attach tip 1 to medium blue bag; pipe window details. Switch white bag to tip 2; pipe small clouds around the airplane.
Hot Air Balloon Cupcakes: Using spatula, spread small amount of white icing into light blue icing to create clouds. Attach tip 1 to brown bag; pipe outline of basket. Fill in the basket with tight vertical lines, then pipe horizontal lines over the vertical ones, leaving space in between to look like a basketweave. Use a toothpick to outline the shape of the balloon. Attach tip 5 to both the medium blue and red bags. Beginning with red, pipe the outer lines, then the blue. Finish by piping a red line in the middle. Using brown bag with tip 1, add small cords to attach the balloon to the basket.