Balloon Badminton: Almost every kid I know loves to play some form of "keep away" with balloons. You know, hitting it up and trying not to let it touch the ground. Well, we developed a variation on it that always results in a case of the giggles. Using fly swatters as rackets, we hit the balloon back and forth to each other like a game of badminton. Sometimes I put A on my bed so he is further from the ground (it's easier for me to get to the balloon in time when it's a higher to start with). And sometimes we use the couch as a net we have to hit the balloon over. I pretend it's my exercise on some days, but it's always great for getting A's wiggles out.
Balloon Puppets: The way a balloon slowly sways and bounces makes it perfect for a silly puppet bobbing his head up and down. We used yarn for hair, pompom for a nose, rubber band for mouth, and a Popsicle stick for the puppeteer to hold. Just about anything will work though: buttons, stickers, paper, ribbon, etc. Find what supplies you have around the house, or simply grab a marker and draw until someone new comes to life. (Markers are A's preference--nice and fast.)
Balloon Balls: I saw this idea on Luckybeans and knew it would be an instant hit in our house. I simultaneously hoped really hard it wouldn't be a disastrous mess too! In the end it was a fantastic, mess-less activity. We made a super large one and a med-small one. World Dad stole the small one to use at work as a stress ball (not that his current job is at all stressful, just boring). We did have fun tossing both of them off the balcony to Solo who was a very good sport about being the target during target practice.
Balloon Science: We haven't done this one yet, but I want to try it soon. We have a two week school break right now, so it's looking like a perfect opportunity. If we do, I'll try to post a photo.
**UPDATE: it was a successful science project. Here are the before and after pictures.