Later that evening Antony called 111 and said his mother had given him some pills.
Ambulance staff attended and spoke to Antony and decided no further treatment was required.
Judge Young said it was unclear ambulance staff had received the message that Antony had taken pills.
Herewini had friends over that night, smoked cannabis and was already intoxicated. She slept beside Antony but when she woke he was unconscious and unresponsive.
Ambulance staff were called and performed CPR.
"But Antony was dead," Justice Young told the court. The post-mortem revealed high levels of methadone in Antony's blood.
Herewini initially said Antony must have got the pills himself.
Justice Young said the family had been worried about Herewini's ability to look after her children.
"The evidence is that you abused drugs, struggled to cope with your children, were involved in a violent relationship and was seriously depressed."
As a mother she was in a position of trust, he said. "Instead of caring for this child, you played a part in his death.
"You had the responsibility of looking after a young child but you could not possibly have carried out that responsibility when you were intoxicated," Justice Young said.
"You then tried to lie and put the blame on your child. There is little about this case to admire."
He acknowledged Herewini's long-term depression played a part in her actions that day.
Some of Herewini's family were in the court, including her parents. She waved at family several times, and made a rude gesture to the Chronicle photographer.
As she was led out of the court, family and friends waved and blew kisses.
Read more: Woman accused of giving son lethal methadone dose named
