Bombs Away!

This is a favorite around here, I just added some food coloring, cornstarch and water to some balloons, (make sure to stretch, and blow up the balloons and then let the air out, to get it all stretched and separated, otherwise the cornstarch will gum up, and you will have blue hands, and a blue kitchen just like me) it was a lot of fun. I filled up all the balloons I had on hand, put them in a bucket, and then we headed outside. 

The kids stood on things of varying heights(obviously adult supervision is required, and nothing too dangerous) and predicted which ones the balloons would splat from, and which ones they wouldn't break from, they also observed that it depended on how much "muscles" you put into throwing it on the ground. 
They really enjoyed it, and I enjoyed watching them use problem solving skills, and make hypothesizes.