You have no idea how strong and tough some people that go to gyms really are. On top of that, the ones that do martial arts are even tougher.
The whole thing in the scenario is that if everything is done properly by the lone hero, he would take out a single 5 year old in one strike. Also, each blow from a 5 year old would not do significant damage to him. This is especially true if he is of tall stature.
Didn't take my time to read all this. But anyone thought of building a kid wall out of the knocked out children? That way, if you make the wall high enough, and from only one side, you can fight them one on one till they're all dead. And if you ever get tired, wall it all up, and just rest inside the dead kid wall till you're ready again. Open up the wall, and kill some more. Rinse and repeat for best results.
I Only read about a quarter of this thread, but I haven't seen this taken into account. Do you know how slippery a basketball court gets when it is wet? Seriously, if there is blood and sweat on the floor, you won't be able to move quickly without slipping. And falling is disastrous. Staying on your feet would be harder than most of you would think.
I haven't read this whole thread, but I would say 30 is way high; consider the whole scenario, not just the headline question. They get to pick the best half of the kids, there's no objects and they don't get scared. They get a day of training and you get an hour.