A mother not only suffocated her son and let him swallow a battery but also drugged her daughter so she could repeatedly take them for emergency medical check-ups, Crown prosecutors say.

The woman, whose name is suppressed, is standing trial in the High Court at Auckland, facing nine charges of ill treatment or neglect of a child.

Opening the Crown case on Monday, prosecutor Melissa Hammer said the abuse of her two young children spanned close to five years, beginning from 2011.

It was then the mother started taking her first born daughter for medical check ups, claiming she was suffering an array of ailments, such as fever, rashes and diarrhoea.

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But with medical experts unable to discover what was wrong, the woman began to claim her daughter was suffering more serious conditions, such as seizures and ataxia, whereby a person loses control of their limbs.

To make it look like her daughter had ataxia, the woman overdosed the girl on medicine and then filmed her in a drugged state so she could show it to doctors, Hammer said. However, the woman's actions then became even more serious with the birth of her son, she said.

She said the woman twice suffocated her infant son and then used her phone to video him while he was in severe distress.

The boy was subsequently taken out of her care as police launched an investigation, but the woman still took an opportunity during a supervised visit to secretly feed him a button battery - common in electronics, such as toys - Hammer said.

The battery had the potential to not only obstruct his airways but give him a chemical burn.

"Fortunately for [the boy], this battery passed safely through him," she said.

However, defence lawyer Susan Gray said the woman never intentionally hurt either of her children.

Instead, she "suffered from debilitating anxiety" and regularly rushed her children into emergency care because she was anxious and over protective.

"She did not at any time fabricate illnesses, she did not at any time cause her children to ingest an object or overdose on medication and she certainly did not suffocate her son," Gray said.

The trial is set down for four weeks.

- NZN