The sportsman allegedly pushed the woman over causing her to fall backwards down the steps.
The mother landed on her wrist, breaking it and she had to spend a night in the hospital.
The children were there when their mother fell and were "distraught", the source said.
The mother and children were interviewed by police a few hours after the incident.
Photos revealed to the Herald on Sunday showed bruising on the woman's right arm, cuts in her legs and a swollen and deformed wrist.
The source said the mother works during school hours but is struggling to make ends meet.
"He left her with nothing. He has remarried and constantly posts on social media all the luxurious places he and his new wife have visited around the world - yet he was paying her a pittance.
"This month the sports star failed to pay for child support and is believed to be in arrears with the IRD. He has stopped payment altogether, it is appalling," the source said.
Police have confirmed that a man was charged with injures with reckless disregard in November last year.
The Olympic medallist has name suppression and has pleaded not guilty. He will reappear in court next month.