A horrified father returned home from work to find his two young children dead after seemingly being smothered and his wife had apparently tried to slit both her wrists.
A 10-week-old baby boy and a one-year-old girl were later pronounced dead after investment banker Jeff Boots made frantic efforts to save them before raising the alarm.
Police arrived at the £1.2million family home, in a well-heeled area of Wandsworth, south London, and arrested Felicia Boots, who did not require treatment despite apparently trying to harm herself.
She is now being held over the deaths of 14-month-old Lily and her baby son. She is being questioned by detectives, who are understood to be investigating the possibility that she was suffering from post-natal depression.
Mr Boots was heard crying out as he returned to his home to find his two children dead.
The young family from Canada had bought the smart five-bedroom £1.2million home just a few days ago in an affluent area nicknamed Nappy Valley because young professionals like to move there to raise children.
Their property, spread over three floors, boasts four bathrooms, has a 45ft back garden and is situated close to Wandsworth Common.
Mrs Boots worked as a hair stylist in her native Canada, but turned to creating her own designer jewellery from her home-based studio under the name 'Pink Tangerine' after moving to London.
Neither of the children had any visible injuries and it is believed they may have been smothered to death. A post-mortem examination was due to take place to establish the cause of death.
Neighbours saw the dark-haired mother being put into a police car by an officer who had an arm around her at around 10.30pm last night.
A neighbour, who did not wish to be named, said that she did not know the family well but had seen the father walking the family dog down the street.
She said: 'I heard him last night, he was obviously upset, it was not really sobbing, but I don't really want to say what I heard.
Another near neighbour told MailOnline: 'The family had moved into the home around 10 days ago and the property still has a sold sign outside.
'The couple were aged in their 30s and they had a pet dog. They arrived with their stuff in vans over a couple of days.
Police said they are not looking for anyone else in connection with the deaths.
Friends of Felicia have written on her website that she is a highly-talented and creative jeweller.
Derek Selby, director of training and development Schwarzkopf Professional, said: 'Felicia is a creative genius. She uses logic to create, but doesn't let it limit her options.
'She can create a simple elegant look for a classic business woman or something so fashion forward for a trendy street kid, it's six months ahead of it's time. Her technical knowledge paired with her creativity allows her to customize something special for every one.'
Peter Kyriacou, owner of Peter Penny's Hair and Beauty in London, said: 'I have had the pleasure of working alongside Felicia for the last four years. Along with being attentive and unassuming, Felicia is very creative and multitalented; this making her a very special artist.'
'Police were called to an address at 7.25pm on Wednesday 9 May.