So the basic rule of thumb is acts which are unlawful and inflict harm upon another person are nearly always actionable, and though there are some questions regarded intent, precedent has established that even the intent to make contact, when executed in an unlawful situation or form, will still make a person liable for damages.
Grievous bodily harm, or any acts which are even capable of causing great damage, can be prosecuted, and apparently win quite often. A schoolroom kick under a desk, for example, that catalyzed a bacterial infection resulting in the loss of use of a leg, could be considered assault because it occurred in the classroom, and was therefore unlawful. Had the kick occurred in the playground in the course of a game, the legal situation becomes much murkier, as there is no real means of arguing that the kick was unexpected by the recipient (consent to accidental or purposeful kicking is implied in schoolyard games, perhaps?) The question I have is what happens if a schoolyard game is understood to continue into the classroom? Perhaps the game can continue clandestinely; if both parties have implied consent to the continuation of the game, does kicking remain unlawful? It is behavior not allowed or permitted in the classroom, so it could still be considered unlawful, but at which point does consent overrule societal/communal expectations?
Furthermore, bodily harm inflicted in the course of a sporting event (a boxing match, say), can be actionable even when consent is given, if the event itself is unlawful (unlicensed or illegal). At some point of physical damage, however, even in the course of a regular, legal sporting event, prosecution must become viable again, right?
Regardless, the number of major, influential cases that involve children getting sued for inflicting harm (under the auspices of assault and battery) is astonishingly large. To a certain extent, I recognize that such cases are likely to be the more confusing and lacking in precedent and thereby unique, but honestly: at some point every vindictive plaintiff has to feel some shame at recalling he/she is suing a child, right?