RedactedNarrative: Unit 1 was returning to the dock in the back of a cove. When the operator pulled back on the throttle, the front of the boat went under water and Unit 1 started to take on water and then capsized to the starboard side. A five month old infant, had on a child's small Type III PFD and did not have the crotch strap fastened. He slipped out of the PFD and drowned. A 9-year old juvenile, had on an adult large Type III PFD. He was trapped underneath the capsized boat and drowned. The boat was overloaded by over 1000lbs. Alcohol/drug use.