The SNP is concerned a 10-year-old was taken to Dungavel this week
Scottish Secretary Jim Murphy has again been called on to stop children being held at Dungavel detention centre.
The Scottish National Party said it was a year since Mr Murphy committed to ending the practice.
The minister announced a pilot scheme offering an alternative to the detention of children of failed asylum seekers at the centre.
But SNP Scotland Office spokesman Angus MacNeil said a mother and her son, 10, were taken to Dungavel this week.
Florence Mhango, 32, and her son Tionge, originally from Malawi, are being held at the immigration removal centre after a raid at their Glasgow home.
Mr MacNeil said: "It has never been right to detain a child behind barbed-wire in Dungavel and there is no excuse for the UK Government's actions this week concerning 10-year-old Tionge Mhango.
"Jim Murphy said last year that these detentions would end - and they have not.
"The Secretary of State must explain why children are still being locked up by his government."
The Western Isles MP said his understanding was that the Mhango family have co-operated with immigration authorities.
And he said: "The UK Government are imprisoning a youngster in a facility that is not fit for children.
"It is an absolute disgrace, and not something that should happen in Scotland today.
"The SNP has had a long-standing commitment to ending this practice and has repeatedly called on the UK Government to act - not only in practice but in law through the UN Convention on the Rights of the Child."
A Scotland Office spokesman said: "The alternative to detention pilot in Glasgow is in the process of being put in place by Glasgow City Council and UKBA [UK Border Agency].
"The Secretary of State said he wanted to see an alternative to detention pilot in place as soon as practical and that is what is happening.
"He has also made it clear that the intention was to reduce the need for the detention of children and prepare families for returning to their home countries voluntarily."
The spokesman added that the courts were the final arbiters of asylum decisions and that the UK Government had a duty to enforce the decisions of the court.