Phil, what i do when i take my 2 youngest is set them up in the same swim, 1 on the left, 1 on the right and i sit in the middle.
if i want to fish i will ledger, you dont have time to float fish.
then i can bait/cast/unhook/untangle either of the kids if needed(the 9yr old can do most of it, the 6yr old struggles at times) all with out moving and rushing about.
if i get a bite the rule is simple, both have to bring their rods in and place them on the ground out the way, it stops tangles and the worry of having 3 fish in the same swim.
being organised is the key, having bait(get them on maggots its cheap, easy, and dosnt matter if you only stay a few hours) baiting tools, nets etc to hand with out moving from the chair.