A mother who suffered postnatal depression has admitted killing her two children at their home.
Felicia Boots, 35, killed Lily Boots, aged 14 months, and her 10-week-old brother Mason in Wandsworth, south-west London, in May.
Her manslaughter plea on the grounds of diminished responsibility was accepted by the prosecution at the Old Bailey, and murder charges were dropped.
She was ordered to be detained at a psychiatric hospital.
The judge, Mr Justice Fulford, said the case was indescribably sad and what she did was a result of psychological forces beyond her control.
A preliminary inquest hearing found the two children had been suffocated.
Her husband Jeff found the children lying side by side on the floor of a walk-in wardrobe when he arrived home on 9 May. She had also tried to kill herself.
Boots, who was in court to enter her plea, gave a note to her counsel Kate Bex to read.
It said: "May 9, 2012 is a day I will be eternally sorry for. It should never have happened.
"It troubles me more than anyone will ever know. Part of me will always be missing.
"I am a good person. I am a good mum and I never meant any of this to happen.
"I am truly sorry."
The court heard Boots had been detained at a psychiatric unit since the deaths and the prosecution's decision followed consideration of doctors' reports.
The couple had moved to the UK in the past few years from Canada.
The court was told that Boots suffered postnatal depression following the births of both children, but appeared to be getting better.
She had been prescribed anti-depressants but had not been taking them after becoming convinced the babies would be taken away from her because of the effects of the drugs on her breast milk.
Edward Brown QC, prosecuting, told the court the Crown had closely examined the medical evidence and spoken to Boots' husband, who was in court.
"This plainly is a tragic case," he said
"There were signs Mrs Boots had made an attempt on her own life. She had marks to her neck."