A woman who gave her two young children rat poison before smothering them was "on the verge of being insane" when she killed them, a court heard today.

The woman, 31, was convicted last month of the manslaughter of her four-year-old son and two-year-old daughter. In February last year, their father returned to their Canley Vale home to find a trail of blood leading into the bedroom. There, he found his wife lying between the bodies of their children. She had tried to commit suicide.

Supreme Court judge Clifton Hoeben last month found that severe depression had "substantially impaired" the woman's thinking at the time.

The woman suspected her husband was having an affair and bought rat poison the day after he told her their relationship was over. She mixed the poison with sugar and water, gave some to her children, then smothered them.

Because legislation prevents child victims of crime from being publicly identified, their mother cannot be named.

As the woman faced sentencing submissions today, her barrister Richard Pontello told the court she was a "caring and devoted mother, who killed her children while severely depressed and on the verge of being insane".

Her thinking was distorted by her mental condition and she believed she was doing the best thing for her children.

Mr Pontello said the woman was "profoundly remorseful" and was still at risk of suicide.

Crown prosecutor Margaret Cunneen, SC, emphasised the vulnerability of the victims. She also reminded Justice Hoeben of the "very affecting and poignant evidence" given by the children's grieving father during the trial.

The woman sat in the dock with her eyes downcast during the hearing. She will be sentenced in November.

Support is available for anyone who may be distressed by phoning SANE Helpline 1800 18 7263; Lifeline 131 114; Salvo Crisis Line  9331 2000; beyondblue 1300 22 46 36.