Devon and Cornwall police have given an update on the investigation into Sunday's speedboat crash in Padstow, Cornwall.
Earlier, it was confirmed that BSkyB executive Nick Milligan had been killed along with his eight-year-old daughter.
Detective Superintendent Jim Colwell said that a 39-year-old woman and her four-year-old son suffered "serious, potentially life changing injuries".
A 12-year-old and 10-year-old girl suffered minor injuries in the accident.
Police have said that the presence of a "kill cord" safety device will form a "key focus" of the investigation into a boat accident in which two people died in Padstow, Cornwall.
The cord's purpose is to ensure that a boat's engine is cut if the person in control goes overboard.
Det Supt Jim Colwell from Devon and Cornwall Police told reporters:
"Clearly the reasons why the boat didn't stop when it otherwise should have done, when there was nobody left on it, is a key part of our investigation.
"The kill cord - the presence of, the state of, and how it was attached or otherwise - will be a key focus of our investigation."
Sky have released a statement after it was announced that Nicholas Milligan, an employee at BSkyB died in a speedboat accident in Padstow.
Andy Hurley from RNLI says emergency services response was outstanding.
The brother of Nick Milligan, who was killed in a speedboat accident described him as an "extremely loving father and husband, son and brother who doted on his family".
The television executive, who was killed in a boating accident in Cornwall, began his career in the South.
Nick Milligan joined Television South in 1983 and moved to Central three years later.
He and his daughter died when their speedboat went out of control at Padstow.
Four other members of the family were airlifted to hospital.
This is amateur footage of the speedboat circling after the family fell overboard at Padstow yesterday
This was a video shot by a member of the public of the rescue operation at Padstow