Navjeet Kaur Sidhu, 26, from Greenford, west London, died after jumping in front of a 100mph Heathrow Express at Southall station while holding her daughter, Simran, aged five, and son, Aman, aged 23 months.
The mother and daughter were killed instantly by the train and her infant son died two hours later at Ealing Hospital.
Mrs Sidhu phoned her husband, Mangit Sidhu, who is in his thirties and works for Royal Mail, who rushed to the station after realising something was terribly wrong, according to a local Punjabi newspaper.
It is believed he arrived in time to see his wife in the distance at the station.
His grey BMW was still parked yesterday at the Sikh temple - the Gurdwara Sri Guru Sing Sabha - next to the station, where he had hurriedly left it to chase after his wife.
Mrs Sidhu had earlier attempted to reach platform one, where the Heathrow Express was due to be passing, by telling a rail worker that she was "taking my children to see the fast trains".
Michael Harrison, 35, a security contractor for Great Western, saw the mother, who was dressed in Western clothing and had a buggy, trying to walk down the station foyer to platform one, which is out of bounds to the public. "I asked her what she was doing and she told me her children liked looking at the fast trains. I told her she was not allowed down there and she accepted that. There was nothing out of the ordinary about her. She must have waited until I had gone so she could go down to platform one," he said.
Up to a dozen bystanders saw the woman as she threw herself and children into the path of the train.
The distraught driver braked when he saw the mother but could not stop in time. He reportedly told investigators: "I knew the person was going to jump and put on the brake but I wasn't able to stop.''
Last night, a family spokesperson said: "The whole family is very upset and shocked and we would like to be left alone. This has happened so suddenly and since there are children involved it has been especially hard. She loved those children more than anything."
Close family friends who run a fish and chip shop minutes from the railway station, said her husband was in a deep state of shock. They said they had not seen obvious cracks in the marriage and described Mr Sidhu as "more than a gentleman''. They said the couple were very modern Sikhs, originally from the Punjab - she had been educated in the UK, while he arrived in the country some years ago.
The mother had always appeared calm and happy to neighbours living near her three-bedroom modern house in Greenford. One neighbour of Pakistani origin who did not want to be named said she had last seen the family going out for the evening in their BMW the night before the incident. The neighbour said: "I saw them on Tuesday evening, going out with their children. She looked pretty and was dressed in black and he was locking the door at about 7pm. I can't believe what happened the very next day.''
The neighbour said she often saw Mrs Sidhu taking her daughter to Allenby Schooland also saw the younger son playing outside the house.
"She came round a few years ago when we had just moved in, to say hello. She told me that they had bought their house. She was a quiet lady with two good-looking children. The little boy would often sit outside in his pushchair while the mother worked inside and he would wave at me.
"She would smile at me but like everyone in this neighbourhood, they kept themselves to themselves. She wore mostly English clothes and her husband did not wear a turban or have a beard. They seemed like a modern, young, happy family,'' she said.
Another neighbour said she had seen Mrs Sidhu two days before her death, returning from nearby Dormers Well Park with her children and their two bikes. She said the family seemed content and they were often laughing and having barbecues in the summer.
One neighbour reported that the husband was seen laughing with his wife after a squirrel was found in their kitchen. Mrs Sidhu was seen screaming and shouting in a jovial manner, according to the neighbour.
But another neighbour said the Sidhus were very private and did not have many visitors. Mr Sidhu would leave for work at about 4am every morning while she would look after the children.