Lincolnshire Police are investigating after two children were threatened in Lincoln, at about 8.45am on Friday, at the junction of Hood Street and Sincil Bank.
A man approached two nine-year-old girls and made threats to them. There was no violence and the children were not hurt.
The suspect was around 6ft tall and was wearing dark clothing.
Lincolnshire Police are appealing for anyone who may have witnessed this incident, or who saw anyone acting suspiciously in the area, to get in touch with them as soon as possible.
Call Lincolnshire Police with information on crime on 101, or call independent charity Crimestoppers anonymously on 0800 555 111.