Teachers confiscated a blade from a four-year-old boy in Northamptonshire according to a shock new study of knives in schools.
Freedom of Information requests to the county police force have revealed 48 crimes recorded at schools over the last five years involved a child carrying a bladed weapon.
Among them, in April last year police were called to an area of north Northampton when a 17-year-old allegedly carried out a knife robbery on school grounds.
On two occasions over the past five years weapon-carrying youngsters were accused of making threats to kill, while one 14-year-old in Wellingborough was accused of causing grievous bodily harm with a weapon.
Another 69 incidents were reported to police but not logged as a crime including one where a four-year-old was alleged to have carried a blade into a primary school in the Rushden area - the youngest age recorded in the study.
Det Supt Dennis Murray of Northamptonshire Police said primary school reports of knives were “extremely rare”.
But he urged parents to keep track of missing household implements that could be used as a weapon.
"Most of these things we are seeing collected are not Rambo-style knives, they are kitchen pairing knives,” he said.
"We would ask parents to take notice of what's missing.
"If you notice a knife has gone from the knife block you need to know where it is."
The worrying figures obtained by Johnston Press Investigations show the number of school knife crimes recorded over the past five years has risen sevenfold - from just two in 2012, to 14 in 2017.
The average age of the blade carrier was just 13, meaning they would be a secondary school teenager in year eight or nine.
Though Det Supt Murray said the rising figures were "concerning", he believes more crimes are being reported to the force because awareness is increasing.
However, he believes the county figures are not a sign Northamptonshire has a gang problem.
"Clearly there are a number of people who we know operate in a gang," he said. "But I don’t see the problems they have in London reflected here.
"When you see one of the incidents involves a four-year-old, it's unlikely that is gang-related."
The police chief urged school to make time in their curriculums for knife crime awareness lessons, adding that local PCSOs are available to give talks in schools.
But the police chief also said the force could do more to tackle the issue and was working with the British Ironworks Centre to create safe amnesty 'bins' around the county.
These would allow people to dispose of potentially lethal blades without fear of prosecution in a locked bin, though he admitted the scheme would not be in place during 2018.
The Johnston Press Investigations study found that more than 2,400 pupils have been caught in school with a knife, blade or other weapon since 2012 across the UK.
The figures show a 42.2 per cent rise in youngsters caught in possession of such weapons over the last two academic years.