My kids (especially Zach) like to do science experiments. This one seemed easy & fun, and I had all of the things we needed for it. Even better!
All we needed were balloons, vinegar, baking soda, and an empty bottle.
We put a lot of baking soda into the bottle:
Then while one of us poured vinegar into the bottle, the other one held a balloon open and at the ready to stick on the top of the bottle:
As soon as the balloon was on it started to fill up!
We did it several times and this was as big as it would get.
Maybe if we were faster as getting the balloon on, it would have gotten bigger? We don't know, but we had fun trying! I think they especially liked the vinegar & baking soda going everywhere sometimes. ;0)