A man armed with knife is alleged to have approached a 10-year-old boy walking home from school.
The boy was walking home on Stukeley Hall Drive in Holbeach at around 3.30pm on Wednesday, July 12.
The man is described as black, around 6ft tall, of slim build, wearing jeans.
He is said to have been holding a knife.
The boy was unhurt and ran back to school.
Specially trained officers will be talking to the child further and there will be an increased police presence near the school.
Anyone with information should call Lincolnshire Police, quoting incident number 321 of July 12.
Alternatively, contact the independent charity Crimestoppers anonymously on 0800 555 111.