Rosemary Perkin, the 35-year-old Nelson woman found dead along with her three young daughters in their home, was an ordinary woman living an unremarkable life in suburban Stoke.

Police believe Mrs Perkin killed her daughters Alice, aged 8, Maria, 6, and 23-month-old Cherie in their beds before killing herself in the basement of their Songer Street home some time over the weekend.

Mrs Perkin, described as a housewife, was separated from her husband, Patrick, who still lived in Nelson.

She grew up in Songer St in a house a couple of doors down the road from where she lived and died, and where her father, Gordon Murphy, still lives.

Mr Murphy discovered the bodies when he called at his daughter's house shortly before 10 am on Sunday.

Police immediately started a murder investigation, but soon said they were not looking for anyone else in connection with the killings. The coroner will rule on the deaths.

Police are delving into Mrs Perkin's medical history as well as analysing a note found in the house for clues to the cause of what they described as "a real tragedy of the highest order."

They would not say how the mother and daughters died. There were no signs of violence or any kind of struggle in the family home, and Detective Sergeant Wayne McCoy said it appeared the three girls had died in their sleep.

They had no cuts or abrasions, and no weapons were found in the house.

"I don't believe that the children suffered," he said.

Detective Sergeant McCoy said police believed they knew what was behind the deaths, but would not give details until after an inquest.

Funerals are expected to be held on Thursday or Friday.

Detective Sergeant McCoy would not give any details about the note, or the family background.

Mrs Perkin was last seen alive on Friday, in Nelson city, although police would not say exactly where she was or what she was doing.

Mr Perkin was in Picton with family.

The clearest picture of the family to emerge in the wake of the deaths was the low-key and ordinary life they apparently lived.

Toys lay on the front porch of Mrs Perkin's neat stucco house as a police team examined it.

Neighbours said Mrs Perkin kept to herself but often walked her two older daughters to Stoke School.

The children were described as friendly and outgoing, often talking to neighbours.

Doreen Payne, who lived across the road from the Perkins, said the girls always seemed happy, clean and well-mannered. Mrs Perkin minded her own business and just got on with her life.

Most neighbours were unaware that she had separated from her husband early this year, although it was widely known that her mother, Beryl Murphy, had died in August after a long illness.

A previous owner of Mrs Perkin's house, Mary Bryant, said she had sent Mrs Perkin a condolence card after her mother's death and recently received a letter back. In it, Mrs Perkin said she hoped to take her daughters to visit Mrs Bryant at Whareama soon.

Mrs Bryant said Mrs Perkin's mother had apparently been a big influence on her life.

Mrs Perkin was an accomplished pianist and had been involved in the Nelson Operatic Society for eight or nine years before stepping back to spend time with her family about three years ago.

Stoke School's board of trustees chairman, David Stephens, said that members of Mrs Perkin's family had contacted the school and asked if it could have representatives at the funerals.

The children were described as "just normal kids" and "good little sportspeople."

Counselling would be available for pupils when they returned from their holidays next week.

Mr Stephens said everyone was devastated by the news and there was a "complete lack of understanding of what's gone on."