Visible crew/equipment: Not long after the main youth characters enter the mine, another boy (the same one they chased through the woods) is followed by the camera from behind as he walks on the tracks holding a torch. The shadow of the camera can be seen just before the shot pans off to the right.
Continuity mistake: When the kids are looking at the Stonehenge-type structures, the younger boy calls for everybody to come and see the hidden message. From the shot in front of the boy you can tell from his body position he's sitting up, however in the next shot from overhead, the boy is now lying down on the rock.