Maybe I should make the combat area necromancer-observed? That way I can pit living combatants in and have them reanimated directly if they don't get pulped.
That works somewhat but I found that having a separate zombie factory is more efficient. Of course if you manage to catch several necros you could have both.
This is what I'm currently doing with zombie production:
1. Have a large room filled with cage traps, with the necromancer chained somewhere with a view to each trapped square.
2. Dump zombifiable corpses and body parts on top of the cage traps, preferably just a single corpse for each tile.
3. Station a member of military within the view of the necromancer.
4. In one or two days the necromancer will notice the hostile soldier (my necro seems to be a bit brain damaged) and reanimates the entire roomful of corpses at once.
5. Zombies instantly get caught in cage traps, without harming anyone or getting harmed before capturing. Rinse and repeat.
Which reminds me: in your experience, are most fatal wounds to living combatants pulping hits to the upper body/head or "and tearing the brain" kinda hits? (important for deciding whether to drop things onto steel serrated disk traps then reanimate the gibs or using them as living dummies first). Also does rekilling sentient corpses seem to count for the "doesn't care about anything anymore" trait?
Children's little mitten clad fists are actually terrible blunt weapons so yes, most of the time they'll pulp their enemies into unreanimatable mess. I'd still recommend having them fight whole creatures/zombies rather than just animated pieces: reanimated hands get destroyed by one hit and zombie heads are indestructible. Better prepare an emergency flushdown mechanism so your students won't fight themselves to starvation.
I have just dumped everything dead to my zombie factory to see which parts reanimate, atom smashing everything that doesn't. It requires a lot of hauling but has worked very well, especially after goblin sieges.
I'm not sure about zombies causing desensitization; all my students are now at "doesn't care about anything anymore" level but that could have come from fighting live enemies as well. I have not observed that part very closely.