Mike is a good juggler, and when his kids expressed an interest in learning how to juggle, he made some kid-size juggling balls out of balloons and rice. The results look excellent!
Instead of buying smaller balls or hacky sacks, I used plans from juggler.org to make several kid-friendly balls. This worked perfectly because I wanted to practice with them while their interest and excitement was high, and together we were able to crank out several balls in about 15 minutes.