First of all, where's kim won bin? Although he survived with the kids in part 1, he suddenly disappeared in part 2 and wasn't even mentioned at all.
Also, what happened to the kids they found in part 1 whose leader had abandoned them? They suddenly disappeared as well.
I coud sense the change of tone/atmosphere of the series from the very beginning of episode 1, instead of the fear and horror the monster creatures made them feel, it was now replaced with fun and laughter..very weird.
And instead of focusing on those creature, no this part focuses on romance between the kids, and non-stop giggling and baby screams.
Finally, what the hell was that ending? Did they survive through all of this to get murdered at the end by their psycho classmate who got crazy because of exams cancelation?!!
For me, part 2 was pretty much irrelevant to part 1 and wasn't necessary at all.