Three members of the same family are in trouble with the police over drink-driving on the same night.

A mother was arrested for being over the limit after collecting her 15-year-old son from Timaru police station.

He was a passenger in a car driven by another 15-year-old allegedly driving at almost four times the youth breath-alcohol limit.

The boy's father, who was also in the car with the mother, was arrested when he tried to drive them home.

The parents this week spoke of their "huge mistake" but accused the police of "entrapment".

The boy's mother, Melanie Humphreys, 35, of Pareora, near Timaru, said she drank three shots of bourbon and three pre-mixed bourbon and cola drinks before going to collect him in the early hours of last Saturday.

"My son went with his mate into town and he was pulled over. He obviously had a couple of drinks because he was over the limit," she said.

"He was taken to Timaru police station and my son and another boy who were in the car were put in the holding cell while his mate was being processed," she said.

"They took his mate home but rang me to collect my son even though he told them I had been drinking.

"He told them 'mum's probably drunk by now' but they still rang and demanded I collect him," she said.

"I know I'm in the wrong. I shouldn't have been driving. But so are the police. They waited until I had picked up my son and was driving home when they pulled me over. I had no intention of drink-driving."

Humphreys was driving her ex-partner Jeff Phillips' car when she was pulled over. He was in the passenger seat.

After she was taken to the police station, Phillips followed in his car to drive them home.

Humphreys said "he hadn't even turned the key" before Phillips was "done".

"I think it's disgusting, it's entrapment. We made the mistake of driving but the police knew I was drinking."

Phillips, 46, who was visiting from Christchurch for the weekend, said he had hazy memories of the night.

"I had been drinking but I didn't think I was over the limit," he said.

He was drinking at Humphreys' house when they got a call from Timaru police.

"Mel got taken back to the station. I waited for her outside and once she was processed I went to drive us all home and I only had the key in the ignition when there was a cop knocking on the window," he said.

"I had f*** all to drink. I think we were deliberately set up.

"It was a huge mistake but we just have to go to court and deal with it."

Senior Sergeant Paul Hampton of Timaru police said the 15-year-old would be dealt with by Youth Aid.

He allegedly blew 529 micrograms of alcohol per litre of breath. The limit for under-18s is 150mcg. The adult limit is 400mcg. Humphreys allegedly blew 776mcg and will appear in the Timaru District Court on July 5. Phillips allegedly blew 559mcg and will appear in court on July 19.

Alcohol Healthwatch director Rebecca Williams said parents had to set a good example for their children.

"This is an example of the inter-generational impact of alcohol use.

"Parents have a responsibility to care and model good practices and clearly that is not happening."