A West Midlands man has been jailed indefinitely for public protection after admitting kidnapping a boy and a girl, aged 10 and 11.
Michael Jackson, who abducted, tied up and sexually assaulted the boy, was arrested last November after the child was found at his flat in Oldbury.
Wolverhampton Crown Court heard Jackson, 50, abducted the girl in the West Midlands in September 2011.
Judge Martin Walsh said the case was "every parent's nightmare".
He ordered Jackson to serve at least seven years before being eligible to apply for parole.
Jackson, from Bristnall Hall Road, pleaded guilty in May to abducting the girl. He admitted charges including sexual assault, false imprisonment and kidnap relating to the boy's disappearance.
West Midlands Police said the boy failed to return home after walking to a shop. His mother then called police and a search started.
The force said neighbours also helped with the hunt and less than two hours later police broke into the flat and found the boy.
His hands had been bound but he managed to escape from a cupboard and move towards a window in the flat, where he was spotted by a woman looking for him.
Jackson repeatedly threatened to kill the boy, who was abducted in an alleyway, and held him prisoner in the cupboard during a three-hour ordeal.
He gagged and trussed up the victim with duct tape and a rope, placed a craft knife near him, and warned him his father would be murdered, the court heard.
'Pliers and hammer'
The judge said: "I am satisfied that had [the 10-year-old boy] not escaped, he would have been subjected to further serious sexual abuse or worse.
"He was, fortuitously, able to escape from the cupboard. When he entered the bedroom, he saw a knife, pliers and a hammer - articles he believed would be used to kill him.
"It is simply impossible to imagine the sheer terror experienced by that young child as a result of your actions."
Debi Gould, prosecuting, said the boy was found after Jackson left the flat in an attempt to construct an alibi.
Miss Gould told the court: "The defendant said [to the boy], 'Don't bother screaming or you are dead - it's time to die if you make a noise'."
She said Jackson put a pillowcase over the boy's head and also told him he would never see his mother again.
The two children were now struggling to sleep and socialise, the court heard.
Det Ch Insp Gary Booth said the case had left the victims and their families "traumatised" and they were "still recovering a year on".
He said: "This time last year we had two normal children.
"They are now introverted and they don't like going out alone."
He said the case had been "totally shocking" and "horrific" and described Jackson as a "serial predator who preys on young children".
Jackson, who was originally called Albert English, was convicted of two indecent assaults in the early 1980s and jailed for 30 months.
His defence lawyer John Attwood said Jackson, who was unemployed and claiming disability benefits, had been receiving treatment under the Mental Health Act.
Judge Walsh stressed that it was likely to be "very many years, if ever" before he was judged safe to be freed from prison.
The abduction of the boy sparked mass street protests in Oldbury, and hundreds of people held demonstrations in the local area, calling for action to protect children from paedophiles.
A community group, called Sandwell United Parents, was set up afterwards and police chiefs praised the group's work to improve communications between residents and officers.