Alright Spider-Mans profile says he can fight for twelve hours straight. 12 hours = 720 minutes = 43,200 seconds. With 100,000 monster kids Peter with his 12 hours of stamina would need to punch out an orphan once every 0.432 seconds to win before tiring out.
I rest my case. The orphan army defeats the orphan.
That amounts to about 2.31 Monster Kids per second.
Surely Peter has ways to defeat multiple Monster Kids per second.
Break one & use its limbs as a projectile.
Chuck one across the battlefield to have it hurtle through others like a bowling ball through pins.
Get one in a web-net he's holding the string of, & swing it around like a mace.
Sling some web to the ground, yank a huge chunk of dirt, then use it as a throwable/pushable mass to crush or bulldoze them.
He could also do something similar to create a big pit & force them into it. To get them in, make a big, wide net of webbing, make a string of web that connects at one corner & the opposite corner. Grab one end, then go to the other end, grab that. He's now holding two horizontally opposite threads by which he can drag a huge net. To tighten it, he can narrow the thread by pulling it in to pull it close.
Jump up high moving backwards, & he now has a huge, pullable net he can drag MKs along the ground with, to either pin them under, trap within, or use to dump them into pits, as well as other set-up.
After all, OP says that each MK occupies 1 square meter, so there probably isn't much distance from the shoulder of one MK to another.
Peter Parker is transported to a parallel dimension inhabited solely by bloodlusted Monster Kids. It is a sunny flat grassy plane wide enough for each Kid to occupy one square meter and has no other structures whatsoever. Peter is in-character but aware that if he manages to defeat all the MKs he will be sent back home, the Monster Kids are bloodlusted. Speed is equalized.
