A "drug-fuelled" woman killed her four-month-old son in Lancashire through gross negligence when she knocked a large television set on to his head as he lay on his mat below, a jury has heard.
Natalie McMillan, 25, was said to be in no fit state to look after her son, Kian, who died from "catastrophic" brain injuries a day later in hospital.
The television toppled off a cupboard as she attempted to move it to plug in a scart lead so she could watch a DVD at the family home in Burnley last December.
Kian's father, Edward Hanratty, 41, was also under the influence of drugs at the time after he passed out on the kitchen floor earlier, Preston Crown Court was told.
Suzanne Goddard QC, prosecuting, said: "The prosecution case is that Natalie McMillan was not in any fit state to look after a child. She had taken heroin and valium and an amount of alcohol. She chose to become intoxicated to the extent that she was not capable of caring for her child in a safe and appropriate manner."
Miss Goddard said the defendant was "careless and drug-fuelled", and that no sober person would have failed to notice the dangerousness of a child's head lying so close to a heavy television.
"Her needs were more important than her child," she said. "The simple step of moving Kian would have saved his life. She showed careless indifference to the life of her child that night. This was not a tragic accident, every parent's nightmare. This was an entirely preventable death. An accident that should never happened."
The prosecution also said that Hanratty had a responsibility to Kian and that he too was in no fit state to look after him and should have ensured someone else did.
McMillan, of Clarendon Road, Leeds, denies manslaughter by gross negligence and child cruelty. Hanratty, of Dirkhill Road, Bradford, denies child cruelty.
The trial continues.