A 13-year-old Picton girl called the police after being assaulted by her mother for refusing to hand over her Ritalin pills so her mother and friends could take them and continue partying.

The girl's mother was sentenced in Blenheim District Court yesterday to three months' home detention and nine months' supervision for the assault, as well as an assault on her 11-year-old daughter.

She was also convicted and discharged for leaving her four children, aged 13 and under, at home without reasonable supervision. She had previously admitted the charges.

The court heard that the mother got in an argument with one of the younger children on March 15 and hit her with the back of her hand before pulling the child by her arm to the kitchen.

Later that night she and her then-partner went out drinking, leaving the children in the care of the 13-year-old.

The pair came home more than three hours later with some friends and continued drinking in their garage.

About 1.30am the mother went to her 13-year-old daughter's room and demanded her Ritalin pills, intending to share them with the people who were partying in the garage, Judge Chris Tuohy said.

The girl refused to hand over the pills and the mother slapped her face several times.

The girl gave her the pills and then phoned the police. When they arrived, the mother and her partner were still drinking and were heavily intoxicated, Judge Tuohy said.

Defence lawyer Rob Harrison said the mother had voluntarily taken up counselling with Te Rapuora Maori health service for her alcohol problems and was also undergoing parenting counselling at Barnardos.

Her children had been returned to her care by Child, Youth and Family, and her partner had since left, leaving her in sole charge of the children.

The woman said she accepted she had to change her behaviour, but Judge Tuohy said he was concerned she did not realise the seriousness of the situation.

"If your children are to have any chance at life, they need to have good support, not a mother who hits them," he said.

- The Marlborough Express