> If you shoot a 'dumb' artillery shell at a target, you lose control of the shell the moment after you pull the trigger. If a group of children subsequently enters the target area...

Nitpick: The children would have to move very quickly to get there during the time of flight of the shell (a few seconds). The interval during which you can intervene is actually the time from the forward observer (remember, arty gunners don't see their own targets) making the call for fire to the time at which the shell is fired. If the notional target is assessed as a high priority (target priorities are pre-assigned), and you trust the forward observer to have checked for collaterol damage, this could be a very short period.

If loitering munitions are used instead of conventional arty, and they can accept targeting updates in-flight, then the interval could be as long as you like (within weapon endurance constraints).

[Edit - clarity]