We got another activity idea out of the Busy Book today. My husband and I thought it was pretty cool but I am not sure it was the best activity for the kids.
You make ice cubes in the three primary colors - red, blue and yellow. Then you put them into three bags like this red&yellow, red&blue, yellow&blue and wait for them to melt. Yep... wait for them to melt. It takes longer than you think. Maybe this should be a summer activity.
I tried to be really laid back and let the kids play with the bags while we waited but I did not succeed. My four year old was pretty rough with the bags and I was afraid they would bust.
Anyway, once they start to melt, you can see that yellow&blue make green etc. In fact, it is really cool because you can still see the two colors of partially melted cubes, plus the new color water in the bag. Like I said, my husband and I liked it. The kids, not so much!