"They had this huge hoist with a fireman on top that was going up and down," she said.
"He was so intent on watching him and the fire trucks."
One of the firefighters invited Hirini to get into a truck, but he shied away from the opportunity.
"He got a bit scared at the last minute," Ms Kershaw said.
Hirini's mother, Tessa Kershaw, said it wasn't the first time her son had been invited to sit in a fire truck.
He had already been in one at Martinborough's Luna Estate, a winery and concert venue.
"He spent a lot of the time running up the hill and sitting in the back seat wearing their actual helmet. That's why he is quite obsessed with fire engines and helmets at the moment."
Tessa Kershaw said the aspiring firefighter had been hosing the garden outside too.
Beach Babylon was engulfed in smoke about 9am today.
Assistant area commander Paul Smith said the fire started behind a wall in the cafe.
"It was quite hard to get to, so it took a while for us to bring the fire under control, and as we were doing that, it sort of developed slightly."
Mr Smith said a lot of old buildings had false walls, and fire could get behind them.
"Especially old constructions like this, through renovations and things like that. Rather than rip it down, they build in front of it.
"What I understand is we had a situation like that [today] and firefighters couldn't quite get to the fire," he said.
Everyone in the cafe and on the upper floors of the building it was in was evacuated by the time the Fire Service got to the scene. There were no reports of injuries.
Six pumping appliances and three specialist appliances attended the scene.
Cafe co-owner and manager Simon Holtham said the fire was believed to have started in an electrical socket - "possibly a faulty plug" - behind a kitchen wall.
"From what the chefs say, that's what they think happened."