If you want fun fantasy swords and magic action with your kids that avoids killing then I add my voice to those saying change the default 0 monster hp = dead body to 0 hp = defeated foe.
There are plenty of models to base your game on. I suggest childrens cartoons. Avatar the Last Airbender, Samurai Jack, He-Man, Thundarr the Barbarian, Herculoids, TMNT, all have plenty of fighting with swords and some magic but generally no body counts.
These are fun, these are fantasy, the heroes get to swing big swords. There are generally no piles of people corpses.
You have options like the Samurai Jack one where you are not having your kids kill people, but robot type stand-ins. Skeletons, constructs, magical outsider demons that go poof are good D&D ones.
You can have the kobolds be stand ins for street thugs and the heroes leave them knocked out at 0 hp, perhaps with a note from their friendly neighborhood spider-adventurers.
You can have 0 hp means the bad guys run away or surrender.