Water balloon surprise!?

So I am planning a birthday party with water balloons, water guns, sprinklers etc and I was trying to think of some things to fill the balloons with other than water. Just a few of them would have a strange filling mixed in with the regular ones. I came up with a few, but it has to be something that wouldnt hurt if it got in your eye, isnt poisonous, and when you thrown the balloon at someone it would break(like if you fill it with flour it wont break) So far I have jell-o and ketchup.