Visible crew/equipment: When Kathy is bringing in the groceries and she asks George where Chelsea is, they run outside to look for her. As the scene goes along it pans past the truck and you can see the reflection of the camera in the truck.
Visible crew/equipment: When George leaves the room after receiving the phone call from Kathy's mother, a boom mike dips into view, reflected in the large ornate mirror at the head of the bed. (00:14:50)
Answer: He sees the balloon, and instantly assumes his step-daughter is inside the boat house, and hence is in danger of slipping and drowning (or perhaps already in such a situation). He rushes straight out to get there as quickly as possible. Checking her room, or telling his wife would take up time, not to mention he is probably running on adrenaline.