The offender fled and Mr Lal chased him before calling police and telling them the getaway car registration and the direction the vehicle was headed.
Mr Lal, 63, who has owned the dairy for 10 years and was robbed at gunpoint in December, said the latest incident had prompted him to consider selling up.
He had already installed security cameras and a smoke machine controlled by a button behind the shop counter, to cloud a robber's sight.
A large stick he bought for protection is tucked under the counter, but it was not enough to make the family feel safe.
"What am I going to do with a stick when he's got a gun? He'll just shoot. It's getting very scary, this business."
At nearby Herschel St Dairy where the alleged robbers drove next, the owner and her 8-year-old son were confronted by the gunman.
The woman, who would give her name only as Mrs Narayan, said she was stunned but not scared.
In 2005, she confronted two youths carrying golf clubs, chasing them off. On Monday she dialled 111, prompting the offender to flee again.
But when the man went to the getaway car it was gone, after the driver was "spooked" by police searching for the culprits following the phone call from Mr Lal. At the same time a neighbour, who had noticed the car speed off when police drove past and then spied the third offender hiding in bushes, also called police.
A dog handler tracked the would-be robber to Russell Ave, and a patrol car followed the getaway car until armed police arrived.
Ngaruawahia police Sergeant Mark Toomey praised the quick actions of residents in helping to arrest the two 18-year-old parents, and the third alleged offender.
He said police were concerned when the young mother got out of the car cradling a baby and Child, Youth and Family had been notified.
"Not the ideal circumstances obviously but the appropriate agencies would take it on board and assess what needs to happen."
Mr Toomey called the alleged robberies opportunistic and said the daylight incidents smacked of desperation.
Yesterday, 21-year-old Rangimarie Dylan Tumai of Rangiriri and 18-year-old Trident James Wilson of Ngaruawahia appeared in the Hamilton District Court, each on two charges of aggravated robbery. They are to reappear in court next month.
An 18-year-old woman was arrested but not charged.