The Wiltshire coroner says the cause of 3 year old Bryn Anderson's death is unclear but has recorded a verdict of unlawful killing.
The bodies of 11 year old Jack and 3 year old Bryn were found next to the body of their father, Graham Anderson, in a flat in Tidworth in September last year.
The coroner earlier recorded a verdict of suicide into the death of Graham Anderson. He said 11 year old Jack was also unlawfully killed by his father.
More top news
Cloudy day, patchy drizzle
Cloudy day, improving tomorrow
Alex Sims, 10, has a rare auto immune disease and without a transplant he will die.