At this age, I'd start at the easy end of the range, the family. People help each other, share, etc.
Next up would be the idea of a town, a community of people that all live nearby each other. They have their own own fire department in case there is a fire, their own policeman, etc.
As far as the bigger picture, nations and cultures and so forth, that might be a little advanced for this age... Perhaps you could just extend this idea of helping each other and sharing a little bit.