Onlookers called 999 after a group of kids were spotted "causing a nuisance" outside the Asda store in School Street, Darwen this evening (December 6).
One boy was arrested for possession of a bladed article after police arrived at the scene.
He was sent to reflect on his behaviour at a detention centre, officers said.
A spokesman for Lancashire Police added: "This sort of behaviour will not be tolerated.
"Please ensure your children are behaving when in public and do not carry knives."
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