A baby girl drowned in a bath after her grandmother left her unsupervised in 14cm of water for two minutes, a court has heard.
Shirley Grenfell was bathing her two granddaughters at her home on Boxing Day in 2017 when she left them unattended to go to her bedroom and Chanelle, aged 11 months, drowned, a jury was told.
Mrs Grenfell, of Illogan, Cornwall, denies manslaughter by gross negligence and a second alternative count of cruelty to a child under 16.
The court was told that the children had stayed at their grandmother's home on Christmas Day night while their parents visited their two-month old baby brother, who was in intensive care after being born prematurely.
Mrs Grenfell, 53, told police she had emptied some of the water after her own bath before putting the two sisters in the tub to wash their hair.
The mother of four and grandmother of 12 then went into her bedroom and put on her dressing gown, leaving them alone for "two to three minutes" before she heard Chanelle's older sister, who was two and a half, shout: "Nanny."
When she returned to the bathroom, Chanelle was "under the water on her back". Mrs Grenfell called 999 and told the call handler that the girl was "lifeless".
One of her sons gave the baby mouth-to-mouth resuscitation and she was rushed to Treliske Hospital, in Truro, but declared dead the next day. A post-mortem concluded that she died from drowning.
Jo Martin QC, prosecuting, told the jury at Truro Crown Court that NHS advice is that babies and toddlers should be put into a bath filled with no more than two inches (5.08cm) of water and should "not be left alone for a moment". She said the bath at Grenfell's house had 14 cm of water in it at the time.
"Shirley Grenfell never meant for Chanelle to die, but she had a duty of care and failed in that duty," she said. "She was being negligent – not just negligent, but grossly negligent."
Simon Laws, QC, defending, told the jury: "Sadly, tragedies and accidents happen. What happened was the last thing that anyone would possibly have wished, a very young child having lost her life in a way that was both tragic and completely unintended.
He added that Mrs Grenfell was "not blameless" but that she "was not taking a risk, she was making a mistake".
Mrs Grenfell denies the charges. The trial continues.