The desperate 12-year-old begged depressed Veronica Bell to think of his two little sisters after she jumped down on to the track at a station.
He had raced to find her on his bike after discovering a suicide note at home.
It is believed the lad talked her into changing her mind.
Veronica, 41, dodged one train, but did not realise another was coming the other way.
As the mum of seven tried to return to the platform she was killed instantly by the 9.14am Sheffield to Manchester train.
The driver blew his horn and slammed on the brakes 100 yards away, but was still doing 50mph at Belle Vue station, Manchester.
He was treated for shock.
The unnamed boys older brother Chris Clark, 19, said: One train came but she couldnt do it. He was talking to her.
"She told him she was scared and it seemed she was going to get on the platform. She had put her bag back up.
Then another train came. She looked round and screamed.
"My brother is traumatised.
The lads father Alan Bell said: This tragedy has had a devastating effect on the family.
Veronica was depressed after being arrested for alleged assault at home in Gorton, Manchester.
Her note told her children she loved them and added: I am going soon.
Police are investigating
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