"These two came out of the blue, jumped over the counter and threatened my wife and another family member with a knife of some sort,'' he said.
"By this stage, my terrified family members went to a space at the back of the shop and that's where one of [the robbers] said 'give me the baby'.
"It was utterly terrifying for them. They locked themselves in a room while the robbers threw whatever they could find in the shop like chocolate bars at the door to prevent them coming out of the room."
The owner had been running the dairy for two years.
He said although the shop was trashed, he was thankful his family escaped unhurt.
"When I arrived three minutes after my wife rang me, she and the other family member were still shaking. I doubt they'll be able to work in the shop again.''
They may need counselling to recover from the ordeal, he said.
Detective Sergeant John Clayton said the alleged offenders were arrested within an hour.
They would be charged with aggravated robbery and be dealt with through the Youth Court, Clayton said.
Dairy staff and an eye witness were able to give clear descriptions of the juveniles and the direction they ran in, he said.
''I'm really pleased with the police response and the result.''
A police dog and handler were still on their way to the scene when the teenagers were apprehended.
An officer with digital expertise was yesterday afternoon examining security camera footage of the robbery.
Anyone who saw anything relating to the robbery is urged to call Whangārei police on 09 430 4500.