In practice, from last year's North Shore Century ride (big ride put on by the Evanston bike club around here):
That's my ear. 9 y.o. is behind and the oldest is the "anchor" there's 2 in front of me here.
Another configuration, same ride:
All in front. Quiet street, long run w/o intersections. The leader (then7) on the little road bike has the great street skills, and a lot of practice with dad- better than some of her older sibs. True, gotta use judgement. I moved up two before we got to the next intersection.
Bigger street, same ride I'm just behind the little leader:
so I do switch around depending on conditions, but I'm never all the way in front. In any event the leader has to follow directions and be able to hold a line.