A 'happy and healthy' four-month-old baby boy died after another child climbed into his cot and fell asleep on top of him.
Noah McCarthy-Bowerman was the victim of overlaying by the other child called Child A, a coroner said.
Senior Cornwall Coroner Andrew Cox recorded an accidental death conclusion and said Noah died from Sudden Unexpected Death in Infancy (SUDI) in a co-sleeping environment.
He told the Truro inquest that there was no suggestion of any intent from Child A or anyone else adding that Child A must not reproach themselves in later life for this most profound tragedy.
Mr Cox said Noah's mother Courtney Bowerman told 999 crews who raced to her home in St Austell, Cornwall, that she had woken around 7am to find Child A in Noah's cot which was at the end of her own cluttered bed.
The coroner said Miss Bowerman lambasted Child A at first before apologising to the child which he found to be a 'genuine response'.
He said: "More likely than not Noah's death has been caused or contributed to by Child A overlaying him. It is a desperately sad finding to make."
A post mortem could not ascertain the baby's cause of death. Earlier Noah's mother told the Truro inquest that she had smoked cannabis on the evening Noah died, but denied claims she was drunk.
And the 25-year-old also categorically denied a suggestion that Noah died after she fell asleep with him on a sofa downstairs at their home.
Miss Bowerman also rejected claims by two friends and a neighbour that she was drunk on the evening before Noah was found unresponsive in his cot and also denied being sick.
She admitted there was a conflict in the evidence but told the coroner:"I was not under the influence of alcohol."
Toxicology tests showed no alcohol in his system 14 hours after the evening ended but there was a high concentration of cannabis in her blood. She claimed she only drank a small amount of lager from a bottle - but the coroner said she had drunk more than she had stated.
He said she had fed Noah after he woke up screaming at 3.04am and put him back in his cot at the bottom of her 'cluttered' bed at 4am on May 2, 2020 - but by 7am she woke to find him unresponsive in the cot.
She said she was sleep deprived and on that night:"I curled up on the side of my bed and passed out, I was exhausted."
The coroner said it must have been difficult to have slept on such a cluttered bed, but Courtney said:"It's not a lie, it's the truth."
Ambulance staff called to the house said a sofa downstairs had been made up as a bed with cushions and blankets on it, an empty bottle of milk next to it and the mother's mobile phone on it.
Miss Bowerman insisted that Child A must have climbed into Noah's cot and she only woke when she could hear Child A giggling and mumbling - but she did not know how long Child A had been in the cot because she did not hear Child A come into the bedroom and climb into it.
Police said following their investigation no further action would be taken against Courtney Bowerman because of insufficient evidence and officers were unable to establish where Noah was sleeping at the time he died.
