A six-year-old boy's mother, grandmother and aunt have been charged after authorities said they staged his kidnapping because they believed he was too nice to people and they wanted to teach him about possible danger from strangers.

The sheriff's office in Lincoln County, Missouri, said the three wanted to scare the boy and enlisted help from the aunt's co-worker, who lured the child into his pick-up truck after he got off a school bus.

Authorities said the man told the boy he would not "see his mummy again", and that he would be "nailed to the wall of a shed", the St. Louis Post-Dispatch reported.

He showed the boy a handgun in an effort to make him stop crying, authorities said.

The man tied the boy's hands and feet with plastic bags and blindfolded him with a jacket, the sheriff's office said, before he drove the boy to his home in the town of Troy.

Authorities said the boy was kept in the basement for a while, before being untied and told to go upstairs, where he was lectured about staying away from strangers.

Police were alerted after the boy told school officials.

According to investigators, the boy's family said they wanted to educate him about the harm of talking to strangers and felt they did not do anything wrong.

The mother is charged with kidnapping and abuse or neglect of a child. The others are charged with kidnapping, felonious restraint and abuse or neglect of a child.

All four are being held in Lincoln County Jail in lieu of 250,000 dollars (£164,000) bail.

The boy is in protective custody.