Fiona Donnison, a 43-year-old former City worker, is believed to have killed Harry, three, and Elise, two, and driven with their bodies in the back of her car almost 70 miles to confront her husband, Paul, at their former family home.
A window at the property was smashed before Mrs Donnison tried to commit suicide. When the attempt failed, she went to a police station and told officers: “I’ve killed my children.”
Officers were directed to her car, where they found the bodies of the children, zipped up in separate sports holdalls.
Post mortem results suggested they were smothered and possibly drugged. It is believed they died within a day of being found. on Wednesday morning.
Detectives are still waiting to interview Mrs Donnison, who is receiving psychiatric treatment at hospital.
Friends suggested that she had recently come under massive strain in her private life.
A family member said that in November, Mrs Donnison’s teenage sons from a previous marriage, William, 15, and Oliver, 12, had left her home to live with her former husband.
Dennis McCrow, 84, her father-in-law from her first marriage, which ended in divorce seven years ago, said that the teenagers had moved out a few months ago.
“My son, Derek, got possession of the boys in about November last year,” he said. “Things weren’t going well between the boys and their mother, so the boys decided to live with their father.
“I don’t know if it was anything to do with the stepfather that came on the scene, I don’t know if there was a bit of a disagreement.”
The mother had also suffered depression after the trauma of losing a baby girl, Mia, to cot death six years ago.
Mrs Donnison split from her husband, Paul, last month and police confirmed that they had “previous contact” with the couple at their home in Heathfield, East Sussex. Sources said that police had been called after allegations from Mr Donnison that his wife was being aggressive towards him.
The source said that no violence had ever been shown towards the children.
A woman who asked not to be named but said she knew Mrs Donnison for many years said the couple had argued regularly.
“I knew it was never going to work between them, it was just not meant to be. They were both so different. I have been around when they rowed”.
The friend said that Mrs Donnison had always adored her children.
“She had been depressed when she lost Mia, but she was a loving mum. She was not like this. She must have completely snapped.”
Family members were “stunned and distraught” at news of the deaths of the two children. Mr Donnison was so distressed that he could not bring himself to personally identify his two children yesterday.
Neighbours told how they had not seen the mother and children for a week beforehand, leading to speculation that she had killed the children several days before she walked into the police station on Wednesday.
Forensic scientists removed what appeared to be a medicine box from the home of Mrs Donnison, in Lightwater, Surrey, last night.
The small plastic box was believed to contain an assortment of tablets, medicine bottles and plasters.
“The previous Monday, she just put the kids in the car and went,” said a resident in Lightwater who did not want to be named.
“She was gone for the whole week. Nobody knew where she had gone.”
Last year, Mrs Donnison uploaded several photographs of herself and Elise on the website Friends Reunited. Under a picture of her daughter, which was placed on the social networking site last July, she wrote: “My beautiful daughter – I know I am biased! ”
In another entry, she said: “I was working full-time until last month in the City as a credit manager for a Lloyds syndicate, and have four wonderful children, Will (15), Ollie (12), Harry who’s two and Elise who is one.”
Writing on a condolence website after the death of Mia, she said: “Our beautiful daughter Mia was born on Sunday 29th June 2003 and was tragically taken from us on Thursday 15th April 2004, a victim of SIDS.”
Mrs Donnison was also a member of a Facebook group called “I love my kids”.
Det Ch Insp Steve Johns from Sussex Police's Major Crime Branch, who is leading the inquiry, said: "I should like to express our sympathy to the family and friends of young Elise and Harry and indeed to all of the community in Heathfield who have found themselves at the centre of this sad event.
"While we may have a suspect in custody on suspicion of the murder of these two young people, I would stress that this will not affect the thoroughness of our investigation or our determination to discover the full facts behind this tragic incident.
"This process is a painstaking one and I would ask for patience while we carry it out. As yet we have not interviewed the woman who is under arrest. She is currently in hospital and we will not be able to clarify significant lines of inquiry until we have formally spoken to her."
well....she lost them
i think that's pretty messed up i really can't see how anyone could do this 
