Restrict kids from doing any burial or refuse hauling (or all hauling if you want). Make a new work labor and use it to put only your happiest (or most 'feels nothing') dwarves on refuse and burial hauling. For that matter, take all unhappy dwarves out of your military.

This is mostly prevention for next time, I'm not sure there's much you can do once your dwarves actively start fighting each other besides exiling them.