About 10pm on Friday night four 8-year-olds playing with fireworks caused a sprinkler to go off at the Napier Dollar King on Dickens St.
A police spokeswoman said police were called by fire crews because the incident was believed to be suspicious.
Four 8-year-olds were found at the scene and police had spoken to their parents, she said.
The alarm activation appeared as though it had been started by the children after they threw a firework into the property.
Napier Volunteer Fire Brigade senior station officer Jamie Nichol said the firework had been thrown through a gap in a roller security door.
The firework did not damage the property but it caused the sprinkler system to activate and saturate many items in the store, he said.
"They were being reckless with fireworks and set off a sprinkler."
Yesterday Mr Nichol said he thought a lack of wind on Saturday night meant there were only a couple of call-outs for the Napier fire service, but thought Sunday night might be busier.
His advice to anyone setting off fireworks was to always have water handy in case of a small fire.
"If it's really windy or in an area that's dry don't do it, it's not worth the risk."
The Hastings fire service also had a quiet night, senior station officer Dennis O'Leary said.
"As long as people are safe around handling fireworks, and children, and ensure any pets are safely put away."
There had been a call-out to a house fire in Mahora, which fire service central communications shift manager Murray Dunbar said had been smoke logged. The cause of the fire was under investigation.
A Hawke's Bay District Health Board spokeswoman said there had been only one firework-related admission to Hawke's Bay Hospital.
A man in his 30s had been brought in on Saturday night, but was in a stable condition. He had been hurt after the sparklers he was holding all ignited at once.
