The first time the teenagers are coming down the emergency stairs in the hospital, the brace on Matt's leg changes from his left to his right leg, and then subsequently changes back to his left leg again.
The goof item below may give away important plot points.
At the end they blow up the boiler in order to cause the whole hospital to be destroyed. Even as the news report says it's an explosion, the stock footage shown is of an implosion. Plus it doesn't even show any flames which would be present if the boiler exploded.