It’s been a while since I read the comic but since neither are wearing horns or have grey skin, it’s either a bad troll cosplay or very likely a kid. I feel like I’d notice say mspaint or postman.
Ok so there are 8 kids possible. Do any of them wear red? I want to say Jane might sometimes? But no props make it obvious. The guy on the right might be wearing the dirk/Dave glasses but I remember those glasses being angular.
How did you come to the conclusion this is a cosplay? It has so few props to make it clear which character is which.