Niamh Marie Mulholland became unwell at her home in Broughty Ferry, Dundee, last Thursday.
She was rushed by ambulance to Ninewells Hospital in the city, where medics confirmed she had died.
It is understood she had been found unconscious in her bed - and her family are asking funeral mourners to make donations to a cot death charity.
One neighbour, who asked not to be named, said: "We saw the ambulance arrive last week. It was quite a shock when we found out what had happened.
"We don't know the family particularly but it is utterly tragic for this to happen to anyone."
In a death notice published yesterday, her family said she was "much loved by everyone who knew her".
The notice read: "She was the cherished daughter of David and Holly, much loved little sister of Eilidh, beloved granddaughter of Dave and Ethel and Janice and Tom."
Niamh's family were too upset to comment at their home yesterday.
Police Scotland Tayside Division said they had been called to the house last Thursday, but that the tot's death was not being treated as suspicious.
A funeral service will take place at 11.45am tomorrow at James Ashton and Son funeral home in Dundee.