Ok so it took me a while to understand why I was failing but I now realize this is a advanced game of spot the difference but you have to play through it a few times to know and remember the other characters.
I think that a bit of interactivity from the characters might be a good way to help the player identify if the character is a monster or a child, as there are very minute differences between the characters that at times seem... contradictory... like the skeleton monster having a blue eye when most of the other kids as monsters have blue eyes under their costume. or one pixel of difference in the vampire eyebrows to their teeth length. I am not saying it's bad but it could do with more directive to determine the correct option.
For a first time experience I might also suggest that adding in some lives would make the player feel less bad about themselves for failing instantly not knowing the various costumes.
I had a fun time once I started figuring things out but a goal or alternative rewards other than score would have been nice.