The little boy looked back at his mother as she desperately screamed for him to move off the tracks, but he thought her cries were part of a 'chase me mummy' game.
He was struck a split second later as the horrified family looked on from the trackside, Peterborough Coroner's Court heard.
Eyewitness Joyce Forrest was picking blackberries near the Fox Covert Road level crossing in Peakirk, near Peterborough, when the tragedy occurred on September 7 last year.
She told the hearing Johnny did not realise his mother's cries were genuine as the 14.41 Lincoln to Peterborough train approached at around 4pm.
Mrs Forrest said: 'Within a matter of seconds the little boy had run out on to the track and looked at his mother. He seemed to be playing a game of "chase me mummy".
'He was playing a game and started to walk across like little ones do, and when he looked at her as she was calling him he thought she was playing a game.
'Then I heard the rush of the train and the mother screaming. She was curled up on the track and was screaming and her other little boy was running around crying.
'The little boy who was struck was gorgeous, with short spiky blonde hair, a lovely round face and a cheeky expression.'
The court also heard a statement from his mother describing how her son turned and looked as she screamed at him to get off the track.
Miss Connors, Johnny's uncle Mr Connors, 18, and his brother Paddy had been visiting members of their family at a nearby travellers site when the accident happened.
Her statement read: 'Johnny just stopped. He turned and looked at me from the other side of the track and I could hear the train's horn.
'I was so close to the train and then the wind rushed passed and the train got him.'
