Sydney mother accused of twice trying to drown baby

Two days later, she again alleged tried to restrict the boy's breathing at another northern Sydney home.

The boy was found unresponsive about 12.30pm on March 21 and was taken to The Children's Hospital at Westmead in a critical condition.

The woman was arrested at the hospital after being spoken to by detectives from the Child Abuse Squad.

She was charged with two counts of attempted murder and refused bail.

The boy died in hospital on March 23, the same day his mother fronted court.

Police expect to upgrade the second attempted murder to a count of murder at her next court appearance on May 18.