That depends. Will they FIGHT or will they just try to swarm me? Will they bite me? Will they try to stick their fingers in my eyes? Where are my boundaries, can I kill them?
Supposing we're on an open field where they can't get away from:
If I can kill them and they will fight me good, I could take about 72 kids.
I would take the first kid I could put my hands on, bite his neck and rip his throat. That's what canine teeths are for.
The rest would tremble in fear, because they just saw I overpower one kid without hasle and kill it mercilessly. Third grades are very poor in organization, only the most apt to sports are, which are just a bunch, I suppose a 10% of the kids are. If I killed one, that would leave me with 8 kids good at being an organized mob and 63 kids that would simply flee.
I'm an adult, so I run faster and am taller than the kids. I would run FROM the sports kids running in mob and I would chase the kids that are running FROM ME. Knocking them over with a knee to the back and killing them with a stomp to the face. If they didn't die, it doesn't matter: they are out of combat and will remain that way - I can get back to them later.
Now, I know I can reach AT LEAST a kid per minute doing this, BUT I would suffer from the burn down and the mob would get me. I would pace myself to kill or almost-kill one kid every 10 minutes.
I can outpace easily the mob, and I can kind of cut my energy expenditure.
Again, I'm an adult. I'm used to go to work and pass 5h without eating and going on breaks, take a 20min break and start over for more 5h without getting upset. Kids don't. That would be their demise.
Getting one kid at every 10 minutes, by the 6h mark, I would have killed 36 freaked out kids. By the 10h30min mark I would have killed all the freaked out kids and only the mob is left.
Kids have a lot of energy but are short of breath, which would make them lag behind me a good deal. I would use that to my advantage.
I would run TOWARD them at full sprint and trample at least one of them. Stop, turn around, repeat. Trample again. And again. And again. Until I have trampled all of them. They wouldn't have died from the trampling, they simply were knocked down, which would space them in their mod. Time to attack.
Kids bones are weak. I would let myself get caught by one at a time and break one leg. After the 8 had their lags broken, killing them would be easy. Ripping their throat would be easy.
Doing this without being grossed is what would be hard.