Police have increased their presence around schools in the north of Kettering after a number of children were robbed at knifepoint on their way home.
It is believed a gang of between three and five teenage boys carried out a series of robberies between Tuesday, February 4 and Sunday, February 9.
In all the incidents, which the police believe are linked, a gang of between three and five youths stole mobile phones from the children and threatened them with knives.
The investigating officer, Det Chief Insp Steve Woliter, said one of the main issues of concern was the increasing level of violence used.
He said: “In all of these incidents, knives have been used to threaten the victims into handing over their mobile phones.
“And it’s particularly concerning as the type of threats and level of violence used against the victims is increasing.
“Additional police officers are now being concentrated in the areas where the offenders are operating.”
But he also said knife crime in Kettering was extremely rare.
All of the robberies targeted children aged between 13 and 15, with the majority happening while the teenagers were on their way home.
The first took place at 4.20pm in Weekley Glebe Road on February 4. The second happened on the same day in Scott Road at about 4.45pm and the third took place on the same day at 5pm in Nelson Street.
The fourth robbery was in Malham Drive at about 4.15pm on Friday, February 7 and the fifth took place in Northall Street at about 2pm on Sunday, February 9.
During the robbery in Northall Street, one boy was hit and kicked in the head and had a knife swung towards his ribs.
In the majority of incidents, the gang asked the children for the time before demanding their phones.
The gang members are all white boys aged somewhere between 15 and 18. A number of them wore hoodies with the hoods up and some had their faces covered.
Anyone with information about any of the robberies can contact Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555 111.