Police said the man told the two children, aged 12 and 14, that if they didn't do as he said they would never see their mom again and that he would kill them.
Police learned of the alleged crime from the mother of the children.
The woman told Windsor police officers that two of her children had been forced by a relative to steal from retail stores on Howard Avenue and Walker Road.
The mother claims she left the two children with an in-law who said he would take them out for supper.
Instead, he allegedly took them to stores and forced them to shoplift.
Police said the value of the merchandise stolen was about $800.
A 23-year-old man has been charged with theft, possession of stolen property, two counts of extortion and three counts of uttering death threats.