A mum died after inhaling lighter fluid which left her baby to die of dehydration, an inquest heard.
Natalie Kane, 27, and her 14-month-son, Harry, were found dead at their home in Whitehaven on December 30.
Ms Kane's family said the deaths were "utterly heartbreaking".
The inquest heard that Ms Kane had previously had a drug addiction and suffered from depression after leaving the Army, but the birth of her son changed everything.
Shane Evitts, her brother, told the inquest: "She suddenly grew up. She was so loving, caring and thoughtful."
Another friend said her friend had "revolved around Harry".
The inquest heard Harry was well cared for.
A few days before Ms Kane died she had tested negative for all substances other than her prescribed methadone.
Ms Kane had also told the Recovery Steps group she was "doing great".
Her friend Stacey Hackett was due to see Ms Kane on Christmas Day but when she didn't return any calls she assumed she was with her bother Harry.
Rebecca Todd, Women Out West support group manager, contacted police on December 30 when Ms Kane did not collect her methadone prescription, which was "out of character".
Ms Todd went to her flat but received no response.
Police found Ms Kane in the living room near a Christmas tree and surrounded by unopened presents.
Tot Harry was found in the bathroom.
Assistant Cumbria coroner Margaret Taylor said Harry died after being "left alone and unable to fend for himself".
She said the case was "incredibly distressing" and had been a "tragedy of unimaginable proportions.
The inquest heard one empty butane lighter fluid canister was found next to Ms Kane and several more were located nearby, as well as two beer cans and empty methadone medication.
A pathologist concluded she died due to butane and propane inhalation while Harry died "probably over a number of days".
Ms Taylor said the purchase of lighter fluid "set in motion unimaginably tragic events" and concluded mother and son had died between December 24 and 30.
