This may be terribly obvious....
But why didn't they just follow the teacher woman out of the cave? She was like, "I can't get a key to let you out" then she would leave and come back
Also, I found the whistle blowing scene hilarious. I was wondering what was next, like maybe he would put her hand in water or something. Man, just imagine the horror of a sleepover!
The past is never dead. It's not even past.