Build a hot air balloon and watch it float
Rubbish bag, straws, thread, cardboard, tape
Find a suitable plastic bag. Smaller rubbish bags can be used if they are very light weight. Such rubbish bags usually boast of high molecular density which usually translates to super thin, cheap, and flimsy. That happens to be what we're looking for. If you don't have any of these you can also use grocery bags.
Attach straws together to form a circle with a diameter of about 10 inches. Do this without glue or tape by twisting one end and inserting the end of that one into the other, and so on.
Tape the opening of the opened bag to the circle of straws. Use light weight tape, and use it sparingly.
Cut a 2 inch square out of thin cardboard like from that of an empty cereal box. Cut four holes near the center (the holes should be slightly smaller than the width of the birthday candles so that they will fit snugly).
Use trick candles for better results, because even if they blow out, they relight themselves.
Attach a twelve inch piece of thread to each corner of the cardboard square.
Insert candles into the holes you cut. You may need to adjust the center of gravity for our cardboard candle holder to hang properly. You may even put the wax on the Cardboard and Stick it on.
Connect the candle holder to the balloon's opening with the four threads from our candle holder so that it hangs down below the balloon.
Make sure it is about a foot away from the balloon.
Light it and let float! You might want to attach a thread or something to avoid it from floating to far if you want to keep it.
Lighting the candles outdoors is the safest option