The kids are mostly having a lot of fun, either because they're doing the zipline thing or because they're getting out of classes and getting to spend time talking to their friends. When they're not immediately having fun they think about lots of stuff.
This kid is worrying about how he's going to fix things for his dead brother, who he reanimated a couple months ago. This kid seems to be thinking exclusively about artistically terrible lyrics for his band. This kid is thinking about spells that he can do to make his parents stop giving him a hard time about not getting his homework done. This kid is worried that his brother is raising some kind of evil monkey goblin in their basement. This kid is in the middle of an elaborate fantasy about raping one of his female classmates. This kid is terrified that people are just - not seeing her, at all sometimes, it's like she's invisible? This kid is missing his friend Willow, who everyone now knows is dead. This kid thinks ziplining is the BEST THING EVER. This kid seems to actually be a zombie. This kid is very clearly suicidally depressed. This kid is plotting Star Trek fanfic. This kid is really worried about the fact that she keeps losing six hours of time on alternating Thursdays because tomorrow is an alternating Thursday. This kid is thinking about whether racecar driving is more or less dangerous than hockey. This kid is periodically thinking about kissing boys and then telling himself that he needs to STOP because that's GAY and he's not GAY. This kid is thinking about asking a girl out but is super worried that she's going to find out that he's half-demon. This kid is worried that someone is going to figure out that his dummy is sentient and has an ancient vendetta against a race of demons. This kid is trying to figure out how she can avoid showering at home, because she doesn't want her foster brother to get sent back to his old house but she thinks he's found a way to spy on her in the shower. This kid is thinking that high school was way less interesting when she went twenty years ago, and also doesn't seem to be a kid.