A mother who was caught poisoning her son at Auckland City Hospital as medical staff scrambled to save the toddler's life has been sentenced to 11 months of home detention.

The South Island resident, who continues to have name suppression, admitted earlier this year to repeatedly poisoning the child over a week and a half in August 2019, including at Dunedin Hospital before he was airlifted to Auckland. Doctors had already warned the family the child may not survive what was then a mystery illness when her tampering with the child's feeding tube was detected.

The mother initially told authorities she didn't know why she did it, but later said it was to bring attention on herself and relieve her of parenting duties. She has a history of mental illness.

During an emotional victim impact statement before Justice Christine Gordon at the High Court at Auckland, the father of the now 3-year-old said he had always been the stable parent and the main caregiver to the children. But his and his children's lives have been thrown in turmoil over the past two years, he said.

"Nightmare is the best word to describe what I and the children...have been caught in," he said. "Having [her] denying her guilt for so long, not allowing myself and my family to get on with our life, is just cruel.

"No amount of anything gives back the sleepless nights and stress that's already been endured. Myself and my children have done nothing to deserve this."

Authorities say the mother searched on the internet for articles such as "child poisoning through eye drops" and "drugs that can kill toddlers because of accidental ingestion" while at the two hospitals with her son.

She administered an ingredient found in non-prescription eye drops stolen from the hospital pharmacy, as well as her anti-depressant medication.

The child was put in an induced coma and suffered brain damage, but these days seems to be thriving again.

"He was very nearly killed," his father said during his victim impact statement. "He went through an awful lot of operations and tests that came with their own risks."

The man said he initially supported his wife, thinking there was no way the mother of his children could act in such a monstrous way. But as the weeks passed, and he realised she was desperately trying to pin blame on him, he came to realise the reality of the situation, he said.

"I was betrayed by [her] — even treated like a suspect in the earlier instances.

"My personal belief is a light sentence will only allow her to manipulate the system...and someday cause more harm."

The father's recollection of the emotional pain their children have gone through was seconded by his sister, who also gave a victim impact statement.

"Because of [her] I have watched continuous hurt," she said. "I've watched my brother and his children's lives get totally destructed.

"My family have suffered and endured enough pain...and deserve some justice."

The defendant pleaded guilty in April to two representative counts of ill-treatment of a child, which carries a maximum punishment of 10 years' jail, and one representative count of theft.

Defense lawyer Julie-Anne Kincade said her client's remorse is genuine. She asked for a sentence of 10 and a half months home detention, pointing out that she has been successfully on bail for the past year and a half.

The defendant believes there is no punishment worse than living without her children and knowing it is due to her own actions, the lawyer said.

"That is what she lives with," Kincade said. "That is what she has to face."

Crown prosecutor Mark Harborow, meanwhile, asked for a four-year prison term.

Justice Gordon referred to the family's ongoing pain outlined in the victim impact statements before announcing her sentence. She agreed with prosecutors' assertion that there will be a long-term psychological impact on the son, which should account for a sentence three months longer than would have been otherwise been ordered.

But she also pointed to the defendant's own abusive upbringing and her mental disorders.

"Your mental health at the time of offending was clearly low," the judge said as the defendant wiped away tears. "It is abundantly apparent you have a complex psychiatric history."

The judge said she accepts the defendant is now taking steps to address her mental illness, and that she is remorseful. She referred to a letter from a family member of the defendant who said she often sobs for hours when she thinks no one is watching, praying for her children.

"Home detention in itself is a serious punishment," the judge said.

Under the conditions of her sentence, the woman will be required to get permission from a probation officer and Oranga Tamariki if she wishes to contact any of her victims. She will also not be allowed to be alone with anyone under 16 years old without another adult in the room to supervise.

The judge approved a protection order against the woman's son.