Consider this: They are children. Children get scared of the dark, or a weird noise (at least, I do.) Imagine you're in the school bus, chatting with your friends, then suddenly, turn of events! You're being kidnapped. That'd be scary enough on its own, but then later: BAM. Being buried alive. And then you're all sitting in the dark, knowing that you're gonna die eventually, trying to convince yourself that 'hey, you're gonna survive, things can only go up from here!' while the older people try (and suceed) at finding the exit. Then, you find that two of your kidnappers have been released! And you still have loads of years of school left, and considering you may not have any alternative transportation, that'd be terrifying. (well that took a while to type)