Foreign Affairs Minister Lawrence Cannon says Canadian soldiers use special measures to deal with young detainees. (CBC)

Canada's foreign affairs minister is refusing to disclose whether Canadian soldiers transferred children suspected of working with the Taliban to an Afghan security unit accused of torture.

Lawrence Cannon says Canadian soldiers use special measures to deal with young detainees, but said sometimes "you can't tell an age."

Questions about young detainees were raised in the House of Commons on Monday after a document obtained by the CBC's investigative unit showed that the Canadian military captured children in the fight against the Taliban, and that many of them were transferred to the custody of Afghanistan's National Directorate of Security, or NDS.

Opposition members peppered Cannon about juvenile detainees, and the minister insisted that the Canadian Forces has "replaced inadequate protocol for prisoner transfer" with new measures.

When Liberal MP Bob Rae asked whether children were transferred to the NDS, Cannon admitted that "it happens sometimes when we can't tell an age."

"If there is any doubt [about their age] they are treated as juveniles," but Canadian troops only detain those who have "attacked or killed a Canadian soldier," he said.

NDP MP Jack Harris said that's unacceptable.

"We're not talking about someone who is 17, 18, 19 — we're talking about children," said the Newfoundland member.

Harris blames military leaders, not soldiers on the ground. "I don't expect soldiers to be experts in international law. I expect them to be advised properly."

The NDP is calling for a public inquiry on detainee transfers, because "Canada has failed here," Harris said.

The report is extremely troubling, given the Omar Khadr case, "which shows they could have done the same to others," said Bloc Québécois Leader Gilles Duceppe.

The secret federal document, obtained through an Access to Information request, reveals Defence Minister Peter MacKay was briefed about young detainees last March.

The document lists how many children suspected of "participating in the insurgency" have been arrested by Canadian Forces, and how many of them have been transferred into Afghan custody. But the information was blacked out.

According to the note, juvenile detainees were being kept in a Kandahar-based, Canadian-run transfer facility for "a significant period."