Police say patrols have been stepped up following reports of a group of men approaching children as they walk home from school.
The reports focus on men in a silver or grey saloon car in the Arboretum area of Worcester and are being investigated by the West Mercia force.
Police say they are advising parents in letters distributed to "all the local Worcester schools".
The correspondence said the force wished to "allay" concerns.
In one of the letters seen by the BBC, senior officers wrote: "Some incidents are reported to have happened whilst children have been walking home from school or in the early evening; or a vehicle has appeared to be driving slowly past schools or children."
The letter continued: "We have an increased number of our safer neighbourhood officers in the area who can answer any questions or address any concerns you may have."
The force added such incidents were rare, it did not believe the reports to be linked, and it was working to "establish the nature and type of offences".