Children as young as seven are carrying knives to school to ward off bullies, police have discovered from visits to primaries.
Other weapons, from ball-bearing guns to knuckledusters, are also being packed in school bags, Merseyside Police said.
At one Liverpool primary, visited by police educating children about the dangers of weapons, half of the 10 and 11-year-olds in one class said they armed themselves to feel safe in school and on their journey to and from home.
Children handed in 43 weapons, including a machete and a hammer, in just six hours when police offered an amnesty. Officers said 30 of the weapons were from secondary-school pupils, but some of the rest were from children as young as seven.
Penknives, which are legal for children to own as long as the blade is less than three inches long, were most common. But the amnesty also uncovered eight lock knives, flick knives - which cannot be bought legally by anyone - and makeshift weapons such as sharpened screwdrivers.
Superintendent Rowley Moore, from Merseyside Police, said: "It's all about protection. All of the children said they would consider using them if they were attacked - they weren't fashion accessories.
"A lot of the kids know it's wrong to carry weapons, but did not realise the amount of trouble they could get in. What we are trying to do is give children the stark and real message to make them sit up and realise that weapons are not the solution to problems, and could lead to them being injured themselves, injuring another person, or facing prosecution."
He said there was no evidence that the use of weapons was increasing in the city, but the results of the amnesty will increase fears that the knife culture among young people is spreading into primary schools.
A five-year-old who was suspended after threatening a classmate with a knife in Kent two years ago remains the youngest person known to have carried a weapon into school.
A study published by the Bridge House Trust last year found that one in 10 boys aged 11 and 12 had carried a knife, rising to nearly a quarter by the age of 16.
Fear of attack was the most common motivation, the report said. Young people were increasingly becoming the victims of crime, but more than half did not report it to police, and 45 per cent did not even tell their parents.
Teachers also failed to report some crimes they had witnessed, the report said.
Following an inquiry into the death of Luke Walmsley, who was stabbed at his Lincolnshire school in 2003, Labour promised to introduce a nationwide knife amnesty within weeks of re-election.
In the Queen's Speech on Tuesday, the Government laid out plans to allow school staff to search pupils for weapons on the authority of the headteacher.
The Violent Crime Bill would also toughen the law on replica firearms and raise the age limit for buying knives and air-guns to 18.
John Mayes, national executive member for the NASUWT in Merseyside, said:
"We do find occasionally that heads come across children who bring these objects into school, sometimes for bravado as much as anything else.
"We have advocated airport-style security checks in some secondary schools.
We do know that there is a growing culture of carrying knives.
"Teachers sometimes say that their school is becoming like a fortress, with security codes and so on. But if you go into any office in the city centre, that's exactly what they have."
THE WEAPONS TAKEN TO SCHOOL
Last year, a poll of more than 4,700 students aged 11 to 16 by Mori for the Youth Justice Board revealed the extent to which pupils were the victims of violence, and were arming themselves to fight back.
* More than a quarter said they had been threatened in the last year, while 23 per cent had been bullied and 13 per cent had been physically attacked.
* 15 per cent said they felt unsafe in school.
* More than half of pupils would tell their parents if they were the victim of crime, but that number is falling. Less than a third would tell teachers, while just 13 per cent would tell police.
* 26 per cent of young people said they would "sort it out themselves" if they were the victim of a crime.
* 49 per cent admitted carrying some kind of weapon in the last year and 28 per cent had carried knives, usually penknives.
* But just 3 per cent of pupils admitted to carrying a knife in school.
* 23 per cent said they had carried a ball-bearing gun, while 2 per cent said they had carried a real, loaded firearm.