Hemsby Lifeboat was launched on Sunday night after reports that a cruiser was sailing the Broads with no navigational lights.
Crew members attended the scene at Barton Turf after receiving an alert at 7.40pm from Humber Coastguard.
The boat was not spotted, but a number of children were seen on the water without lifejackets.
Coxswain Daniel Hurd said: 'There were a lot of vessels down there so there would have been a high risk of collision.
'If you are hiring a boat take on board safety advice.
'There were also a lot of youngsters with no safety jackets - we see that all the time and it is crazy.'
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