According to reports, the girl placed the needle in a strawberry and showed it to friends at her school, the Daily Telegraph claims.
One student told teachers and the police were called. They reportedly interviewed the girl at her home and she eventually confessed.
'Obviously, in the last few days we found a young person has admitted to a prank, including putting needles in strawberries,' the police commissioner told reporters in Sydney.
Mr Smith said the child would be dealt with under the youth cautioning system.
It comes as the Attorney-General said there had now been more than 100 reported cases of sabotage across the country, with the scare emerging in Queensland and spreading to Tasmania and Western Australia.