I was talking to my 11 year old grand daughter about your situation. The first thing she asked is if they blocked the door to the sleeping hall with the dead bodies. Then did they set traps or a watch? She has only been playing for 6 months in a weekly game. I just found it interesting that she agreed with your 1st grader, where the older ones didn't understand it.If they continue then maybe just kill one of them(make sure there is a way to res the fallen and they know about it).
You might also suggest to the casters to buy some wands. That way they can save their spells and not need to rest so much. Even non casters can buy healing wands and let a caster use it to heal them during or after battles.