More details can be published about a man charged with murdering a 2-year-old girl after his trial started today in the High Court at Auckland.

Aaron Archer, 30, is charged with murdering the girl at Mangawhai almost a year ago.

Until today the child's name and her relationship to Archer could not be reported.

The Herald can now reveal the child was Ariah Dawn Roberts.

Archer was Ariah's mother's boyfriend at the time of the alleged murder.

Ariah's mother's name has been suppressed.

But Justice Christian Whata today allowed media to report the other details of the case including, for the first time, the little girl's name and the fact that Archer was effectively her stepfather.

Police were called to a Mangawhai address at 8.15pm on August 22 last year.

Initially Archer was charged with assaulting the child.

It is understood Ariah was a twin, but her brother tragically died at birth.

This morning a jury was selected and Justice Whata addressed them, explaining the court process and their role as jurors.

He then adjourned the trial until tomorrow, where Crown prosecutor Brian Dickey will present the case against Archer.

Archer was supported in court by a number of people today.

The trial is expected to take about two weeks.