To answer your question, no I didn't do my kid's project. I helped, and that's why the day rocked hard.
We spent the day brainstorming, planning, testing, and moving things around until she found a design that actually popped the balloon (the end goal.) We helped her figure out which simple machines would work. And in the end, she managed to pull a lever which released weights, which pulled up a balloon full of baking soda up to dump into a coke bottle full of vinegar at one end while releasing a steel ball at the other. While the chemical reaction in the bottle filled the balloon with air, the ball went down two tracks, into another bottle, transferred to an inclined plane with switchbacks, and hit a Lego car which set off a chain reaction with books, which pulled a string to release the toy plane with a pin in the tip to pop the now inflated balloon. Five hours of pure family time in exchange for 20 seconds on tape and a science grade. And I wouldn't trade it for anything.