When the guards from the lodge are walking the 2nd Massachusetts kids' security team away, they pass a lone tree and approach a pickup truck. The camera cuts to Ben, who is watching from the soccer field. Several seconds later, the camera returns to the men walking away, and they are again passing the same tree.
When the group of kids escape the camp and reach an abandoned house there is a helium balloon that's fully inflated. In this part of a time-line that helium balloon should have been deflated in about a week or two, like the other rubber balloons on the wall after a day or two.