Both boys were kept hostage for three hours after 28 year-old James Cross grabbed them in Oxford Circus, central London, and claimed he had a knife.
Cross made the boys, aged 14 and 15, take turns to rob passing women, keeping hold of one and threatening to stab him unless the other returned.
Jailing Cross for a minimum of three years, Judge Ruth Downing told Cross his victims had a 'genuine belief' they would be hurt unless they followed his instructions.
She said he "wept for humanity" after hearing how a shopper laughed at the pleas on one victim. She did not believe he was being forced to mug pedestrians.
She said: 'This was not only a very unpleasant and frightening experience for these young men - it is also deeply worrying because of your continued attempt to contact the young men after the offence finished.
"It speaks to me of a great lack of understanding of the seriousness of your conduct and its effect on other people."
Reflecting on the woman's refusal to help, the judge added: "I weep slightly for humanity."
Croydon Crown Court heard Cross has a previous conviction for possessing child pornography.
He approached the two boys close to the entrance of H&M at the junction between Regent Street and Oxford Street at around 1.50pm on March 17 this year.
After grabbing one of their arms and asking if they had any money, he demanded their mobile phones, adding: "I've got a knife".
He led them to an area near the Royal Academy of Music, Marylebone Road, where he took photos of them on his mobile phone and ordered them to each bring him £20 by taking turns to mug people.
"You have to go and snatch a bag from a woman," he told one of the teenagers.
Instead of robbing people, both boys took cash from their own wallets and pretended the money had been stolen from passersby.
Paul Jackson, prosecuting, said during the afternoon one of the youngsters asked a woman for help 'but unfortunately she didn't believe him and laughed.
"They were absolutely petrified and didn't run away because they feared serious repercussions," he said.
"Both victims were extremely scared."
One of the boys was made to take back shoes he had bought earlier that day and then give Cross a cash refund.
After some three-and-a-half hours and visits to Tottenham Court Road and a council estate, Cross let his victims go - before bizarrely shaking their hands and wishing them luck with their school exams.
Both later received a friend request on Facebook from the same account, thought to have been linked to their abductor.
He was caught after calling one of the boys at home without withholding his number, allowing police to trace the call.
In a statement, the 14-year-old said: "He told us he would take us back to his house, where he and a friend would 'have some fun with us'.
He added: "It plays on my mind. I'm worried if the suspect is not sent to prison he will come to find me."
Echoing his fears, the 15-year-old said: "At one point some police officers walked past us, and he threatened he would kill us if we drew attention to us.
"I believed him. I believed he wanted to abduct me and do things to me, and this was terrifying.
"When I'm out and about, I worry there are other strange people like him out there, and I don't feel as safe as I used to"
Judge Downing said both teenagers had "conducted themselves with considerable bravery during what must have been a deeply distressing experience".
Cross, whose previous convictions include robbery, arson, and making death threats, was declared a 'dangerous' offender and will not be released until he is considered by the Parole Board to have reformed.
Cross, of Brockley, southeast London, admitted two counts of kidnapping and two counts of robbery.