Here's another great kid's activity, that can be modified for younger or older kids. I used this for my 9th grade Physical Science students when teaching them about thermodynamics.
I found that any lab that involved food was sure to get them excited and motivated to learn! And this one involves ice cream!
So, we waited for a really warm day, divided into groups (necessary to give freezing hands a break as they pass the bag off), and headed outside to learn about thermal energy and enjoy a cool snack!
Just make sure you have them tell you the principles behind the lab before allowing them to dig in!