One child to a target at a time. Two children can mean one is jerking arrows out of the target while one is standing impatiently behind. Teach them to pull out the arrows with their thumb towards the target, not the bottom of their fist, that breaks and bends arrows, but it's natural to them. They should stand to the side of the arrows when pulling them. This must be taught.
Arrows can come out with sizable force.
Even at the one pulling them. Look for the one you missed. Then shoot again. Use the whistle. Arrow lengths are extremely important.