A Sydney mother who blamed her boyfriend for enforcing a regime of violent discipline against her seven-year-old son had a history of neglecting her children and was recorded repeatedly slapping one of them on a train just weeks after meeting the man, a court has heard.

The accusations were made against mother of three, Kayla James on Wednesday as she gave evidence against her former boyfriend Kodi Maybir, who is on trial for the murder of her seven-year-old son.

Kodi James Maybir: Guilty of murdering a seven-year-old boy.

The murder trial has heard that James is already serving a minimum 10 year jail sentence for manslaughter over the son's death because she effectively left the little boy to die after he was allegedly assaulted by Mr Maybir in the days leading up to May 21, 2013.

​James has told the court that while she had treated her children "very well" before moving in with Mr Maybir, he then encouraged and pressured her to participate in his violent punishment methods.