Ministry of Justice staff are apologising to a grandmother who wasn't sent a coroner's report on the death of her mokopuna and saw it in news.
The report found Sapphire Williams who was two months old, died with an alcohol level in her body more than six times the limit for an adult driver.
The finding prompted a coroner's warning about the dangers of breast-feeding when a mother has been drinking.
Coronial Services says the case manager was supposed to send the inquest report to the baby's parents, at two different addresses, and to the grandmother, Moira Tua.
But the staffer forgot to send the report to Mrs Tua, and one parent's report was returned to sender.
Ministry of Justice spokesman Chris King said the error and the distress it caused were regretted, and staff would be in touch with the grandmother to offer a personal apology.
Alcohol level six times the limit
Sapphire died in January 2017 with a high level of alcohol in her system.
A toxicologist's report found the baby's blood alcohol level was 308 milligrams per 100 millilitres of blood - a high reading that prompted a second test, but returned the same results.
It was more than six times the legal blood alcohol limit for driving.
The doctor who completed the post mortem, Dr Simon Stables, said the alcohol findings were difficult to explain as there was none found in the stomach, just around the heart and liver of the baby.
The coroner, Debra Bell, found Sapphire Rose's direct cause of death could not be ascertained but noted the very high level of alcohol in the baby's blood and a dangerous sleeping environment were significant contributing factors.
Her mother, Janice Tua, accepted the alcohol in Sapphire's system most likely came from her own consumption.
She had been drinking the night before her daughter died and believed she would have consumed 18 cans of pre-mixed bourbon and cola.