An independent investigation into the death of Aaron Egan has criticised East Ayrshire Council over its handling of their case, although there was an acceptance his death could not have been anticipated.
The five-month-old boy, referred to as Baby E in the report, drowned in the bath in Kilmarnock on July 17, 2010.
Parents Thomas Egan and Chrystine Templeton, who are not identified in the report, were originally charged over his death but the case was dropped.
The new report has found East Ayrshire Council removed Aaron from the child protection register and reduced the number of visits to his Kilmarnock home. The Significant Case Review found the council and other agencies missed opportunities to intervene.
The report states that Aaron's mother was the subject of a "high risk pregnancy referral" from social services on August 8, 2009.
Two days after his birth on February 6, 2010, the baby's name was placed on the child protection register under the category of physical neglect.
He was discharged home on March 22, 2010 with a support plan in place, including "addiction support" for both parents.
The report reveals that social workers tried repeatedly to gain access to him, but only half of their visits were successful - and visits were cut thereafter. Despite further problems with home visits it was decided on April 26 to remove Aaron's name from the child protection register as "the family was engaging well with the agencies involved".
The report found the baby should have been in care from birth, that family support opportunities were missed and that information about Aaron's parents' lifestyle should have been shared more effectively. The independent assessment found there was a lack of recording of the decision-making process - including the rationale for the decision being made for the child to go home.
The review also said the death could have been prevented if the parents had "fulfilled their parental responsibility" and had not left the baby on his own.
While the report makes 17 recommendations for change at the council, it confirmed that no disciplinary action has been taken against any staff member involved.
It said a range of improvements and developments had been introduced including a new electronic information sharing system, Ayrshare, to assist health, education and social work staff to share information, "enabling progress to be monitored and reviewed more effectively".
Susan Taylor, chairwoman of the East Ayrshire Child Protection Committee, said there has been a "determined effort" to understand and learn important lessons from the tragedy.