A six-year-old boy died when he plunged from the eighth floor of a tower block.
A woman, two men and a teenage girl were arrested on suspicion of neglecting Liam Shackleton, who fell from the window of a flat in Leeds.
The four were later released on police bail pending further inquiries, West Yorkshire Police said.
Social workers were not involved with the family but the city's Safeguarding Children Board said it is planning to oversee a review into the circumstances of the death.
Neighbours said the youngster moved into the flat in Lindsey Mount recently along with his parents, Martin and Tanya Shackleton, and two brothers and sister.
It is understood Mr Shackleton's father was the tenant of the property.
Speaking to ITV News, a devastated Martin Shackleton said his son had ADHD and described him as "hyperactive".
He said: "I'm in bits. I heard the news yesterday teatime and I've been in a right state ever since."
Police would not confirm the identities of the people who have been bailed. A force spokesman would only say they were two men aged 57 and 36, a 28-year-old woman and a 16-year-old girl.
Jane Warden, 51, a care worker, said she saw Liam on the ground after he fell. She said: "He was lying, face up, with his little arms and legs all twisted."