A 65-year-old meth-addicted grandmother in New Zealand is facing trial for allegedly killing her grandson, aged two because he was too hard to toilet train.

Kathleen Cooper threw the toddler down the hallway of their Manurewa home in Auckland following a toileting accident on 13 December 2015, prosecutors told the High Court during a trial on Friday (11 August).

Prosecutor Aaron Perkins QC told the court that the child, Jermain Ngawhau, suffered severe head injuries after the incident. He was rushed to the hospital for emergency surgery but died five days later.

Perkins further said that Cooper had volunteered to take care of her troubled daughter's four children - all under 5. However, she became irritable from smoking methamphetamine and used to beat the children regularly.

The victim was reportedly found with old bruise marks. The prosecutor told the court that Jermain's delayed development made him slow to learn to use the toilet and thus he received a regular beating from his grandmom.

A witness told the court that the day before Jermain's death, Cooper was seen swearing at the child and then dragging him naked by an arm.

Cooper's lawyer, Paul Dacre QC, meanwhile admitted that she killed her grandson, but argued that she did not intend to kill him and should not be convicted of murder.

Perkins, however, responded saying that Cooper was aware of the dangers of throwing the toddler and the past incidents of beating the kids showed that she understood what could hurt them. He also said that medical tests showed that the children were also exposed to methamphetamine while she smoked the drug in the house.