The other day we unexpectedly ran into Frieda and Rose at the park. The four kids first acted out an elaborate scenario involving putting people in jail.
Then they proceeded to work together to push each other around the field in a broken down plastic car
The car pushing was really quite awesome - they would push for a while and then have to stop so Noah could adjust the front wheels (it seems that he was the only one that really understood the concept of steering). But even with that small setback they played at this for a long time (with no parental help at all) and all four of them got a turn. Rose and Frieda may have pushed Noah in the car into a fence.. but happily no permanent damage.