Children are alleged to have been tied up and insects, a snail and a spider put in their mouths at a Porirua house.

The parents of eight children have gone on trial in Wellington for neglecting them and committing sexual offences against them.

As well as sexually abusing the children, the father, 55, is accused of tying the children to a clothes line at their home and spinning them around.

He is also accused of using a knife to sexually assault three of his daughters and tying up some of the children and putting insects, a snail, and a spider in their mouths.

In the High Court at Wellington today prosecutor Geraldine Kelly said one of the children was raped on the kitchen table while the mother, 42, watched and two "uncles" took part in the abuse.

The mother is also accused of sexually assaulting both her daughters and her son.

The parents and "uncles" aged 39 and 56, have name suppression.

They have pleaded not guilty to a total of 51 charges.

Justice Alan Mackenzie has told the seven men and five women on the jury that they would hear some very distressing evidence during what is expected to be a three week trial but they should not allow their emotions to affect their decision making.

Defence lawyers say the accused will deny sexual offences or violence took place.

Noel Sainsbury, the lawyer for the father, said there were aspects of the lifestyle and parenting that were "simply not good".

But a dysfunctional family did not necessarily amount to criminal behaviour.

Greg King, acting for the mother, said the family situation was " a million miles away from an idyllic family" but there was no deliberate neglect.

The mother had her own difficulties and limitations including illiteracy, but the children had adequate food, education and healthcare, although they were not receiving more than the basics. The jury might think the mother was struggling to deal with all the children, one of whom had serious health problems.

He asked the jurors not to allow themselves to be overwhelmed by the "tale of woe and misery" that would unfold in court.

Liz Hall, the lawyer for one of the "uncles", said the man was an alcoholic who went to the family's house for drinking sessions and denied any kind of sexual touching or violence towards the children.

Lawyer Paul Surridge, for the other "uncle" said the children did not come from a rosy home environment and might be saying some things to get attention for their plight.

The evidence came from dysfunctional children who were either untruthful or unreliable, he said.

Outlining the Crown's case Ms Kelly said a Child, Youth and Family Services social worker had been involved with the family since March 2006 but it was not until March 2010 that they were removed from the house.

Now aged two to 13 the children were left to fend for themselves while their parents and two regular visitors to the house - who were known as uncles but were not related - drank, sometimes from morning to night.

The children were feeding themselves and caring for each other, even though the youngest had special feeding needs due to a physical abnormality. They did not have enough food or adequate clothing, often went to school hungry, and one had scabies when she was seen at hospital after being removed from her parents care.

A midwife would give evidence of the mother drinking alcohol when she was pregnant.

"When they did get attention from the adults it was the type of attention no child should receive," Ms Kelly said.

The children have cognitive difficulties and cannot concentrate for more than about 15 minutes at a time so the trial is likely to be frequently interrupted for short breaks while they give their evidence.

- © Fairfax NZ News