Its claimed children and teenagers in Grimsby are risking serious injury or death - by breaking into some of the town's derelict buildings.
The council says in one of the most recent cases three young people were spotted in a building on Eleanor Street.
The fire service had to be called out after a blaze was started, potentially putting a rough sleeper inside the building at risk.
With half term coming up parents are being told to be aware of where their children are going.
Humberside Fire Service say some of the buildings involved are 'death traps'.