Image copyright Lincoln County Sheriff Image caption Denise Kroutil allegedly asked a colleague to help kidnap her nephew

The family of a six-year-old US boy staged his mock kidnapping because they thought he was too nice to strangers, Missouri police say.

The boy's aunt, Denise Kroutil, allegedly asked a colleague, Nathan Firoved, to help "scare" her nephew.

The boy was lured into a car, taken to a basement and told he could be sold into "sex slavery", police said.

Ms Kroutil, Mr Firoved and the boy's mother and grandmother, who allegedly also took part, were arrested.

"Family members told investigators their primary intent was to educate the victim and felt they did nothing wrong," a statement from the Lincoln County Sheriff's Office said.

Police said Mr Firoved lured the six-year-old into his vehicle after he left a school bus in Troy, Missouri.

The man told the boy he would never "see his mommy again" and would be "nailed to the wall of a shed".

Image copyright Lincoln County Sheriff Image caption Mr Firoved allegedly threatened the boy with a gun as he drove him around in his vehicle

Mr Firoved allegedly showed the boy a handgun as he was crying, threatening him. He then covered the boy's head with a jacket, bound his hands and feet, and brought him into his own basement.

In the basement, Ms Kroutil allegedly took off her nephew's pants and told him he could be sold into "sex slavery".

Eventually he was unbound and given a lecture about strangers, police said. The boy's school called child protective services when he told them what had happened.

Mr Firoved, Ms Kroutil and his grandmother, Rose Brewer, have been charged with kidnapping, restraint, as well as abuse and neglect of a child.

His mother, Elizabeth Hupp, has been charged with kidnapping and abuse and neglect.