Read the bible story of Peter and Cornelius (Acts 10:1-11:18). I read from a very old copy of the Egermeier's Bible Story book. While reading the story, I would stop and really make sure they were understanding what was being said. And what this had to do with cooperation. It was a tad difficult because of the custom of Peter, being a Jew, to not enter a Gentile's house. I think this part was difficult for the boys to grasp.

Made a list of some of the jobs each person in our family does. What would happen if Joshua stopped unloading the dishwasher? Or Martin stopped going to work?

Discussed the old saying "many hands make light work". Using the job of grocery shopping, I was able to show the boys how just using my two hands would make putting away the groceries go very slow. But if Martin helped (now we have four hands working together), it would go quicker. Then if Joshua and Caleb joined in (a total of eight hands - um, a little math throw in too) would make the job go even faster.