This is a possible session for fell running or orienteering:
“Here is a fun pursuit workout that you can do on the track. Divide your runners into two groups of equal numbers on opposite sides of the track. The athletes should then run at easy endurance pace in a single file line. At your whistle the front runner in each line should run at sprint pace until they catch the group in front of them. As soon as the chase runner from each group reaches the group in front of them blow your whistle again to send the next front runner on the chase. Continue this for the duration of your workout. I would suggest a distance of between 2 and 4 miles.” From this website.
This could be modified to work with 4 groups around a square, marked route on grass or in terrain (for orienteering). If there are four adults available for accompanying the groups then they can set the steady pace.