Social services missed chances to protect a four-year-old girl who died after being fed prescription drugs by her own mother, a serious case review concluded.
Poppy Widdison, from Grimsby, died in 2013. Her mother, Michaela Pyke, and her partner, John Rytting, were found guilty of child cruelty and are due to be sentenced next week.
Their trial heard they encouraged her to eat sedatives, including diazepam, because they saw her as an inconvenience. The jury heard tests had found the child had taken significant amounts of heroin and methadone in the months before her death.
The report published by the North East Lincolnshire Local Safeguarding Children Board identified a "number of missed opportunities" to protect Poppy both before and after she was born.
It said Pyke (37) led a "chaotic lifestyle" that was "incompatible with safe parenting".
Pyke was addicted to drugs since her teenage years and was suspected of "drug-dealing; allowing violent drug dealers to live at her home, avoidance of professional agencies and an inability to establish children's routines", the report said.
It said she had a "long history of non-engagement with services" and "managed to mislead professionals with apparent ease". The council was not aware of the extent to which Poppy was exposed to harm, it said.
After she was born, Poppy was going to be put into the care of her paternal grandparents, but in the end her parents retained parental responsibility.
The report described the plan that was in place to ensure Poppy's safety as "naively optimistic".
Pyke had already had her first child taken out of her care five months before Poppy was born.
When the little girl was three years-old, a relative told children's services that her mother was smoking cannabis and "lying in bed" while leaving her daughter on her own. But no action was taken after "no further evidence" was found to substantiate the allegations - despite the fact that it has since emerged that at the time Poppy was being given drugs.
North East Lincolnshire Council said it accepted the findings and had implemented an action plan in response to its recommendations.