This comes less than ten days after 26 girls were recovered from a Mumbai-bound train.
A senior police official said that in Bokaro, the boys were made to disembark a Kerala-bound train around noon.
"All six of them, including three maulvis, were taken into custody after they failed to produce any document to support their claim," he said.
The SP said the children, aged around 7-8 years, were handed over to the Child Welfare Committee (CWC).
Meanwhile, a senior RPF official in Bokaro said that the boys were in the age group of nine to 17 years. While some were scheduled to deboard at Vijayawada, some were to deboard at Coimbatore, the official said.
Vinay Ayog, the chairman of CWC unit in Bokaro, said that initial evidence suggested that the children were being "trafficked" out of the state.
He, however, said that the police were still investigating into the matter.
"We are assessing whether government guidelines were followed while ferrying the minors. The police in Jamtara district have been contacted for identifying these children," he added.
"The police would able to give details about the case after questioning the six men, who have been taken into custody," he said, adding that the Bokaro police had informed Ranchi childline about the development.
Rupa Verma, the chairperson of Ranchi CWC, said all 21 children, aged between six and 15 years, were shifted to a shelter home in the state capital.
On July 5, 26 underage girls were rescued by the GRP and RPF on board the Muzzafarpur-Bandra Awadh Express after a tweet from a passenger alerted them to the situation.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)