Here’s some simple science to go with “for every action there is an equal and opposite reaction.”
Copy rockets or stars onto cardstock. Have the kids color the star or rocket. Cut it out and tape it to a coffee stir stick. Slip the stir stick with the star/rocket attached into the end of the straw. Blow the open end of the straw and the star/rocket will fly out. If you are working on counting backwards, make the rockets and count down before they shoot them off. You can experiment with this by using different paper which changes the weight and therefore the distance the object flies. You can also add some math by measuring how far the star/rocket flew. You can also make a “moon” out of paper and see if the kids can get their rocket to land on the moon.