The UK's four children's commissioners have written to the Government to tell of their "deep concern" at the decision to end a scheme to bring lone child refugees to Britain.
The Government last week unexpectedly announced that just 350 children will be given a home in the UK under the so-called Dubs amendment - far lower than the 3,000 campaigners had hoped for.
The move has sparked widespread outcry and the children's commissioners of England, Wales, Northern Ireland and Scotland have written to Home Secretary Amber Rudd urging her to rethink the plan.
They tell of their "deep concern" at the decision and urge Ms Rudd to "consider carefully the plight of the many thousands of lone child refugees in Europe who are currently at risk of exploitation and trafficking".
They add: "The Government made a welcome commitment through the scheme to taking some of the most vulnerable lone child refugees who are rootless in Europe.
"The number that have been brought to the UK under the scheme thus far falls significantly short of expectations and we consider that, as a signatory to the UN Convention on the Rights of the Child and the Optional Protocol on the Sale of Children, the UK should play a far greater role in both offering protection and security to lone child refugees in Europe and in resolving the crisis that children are facing in Europe, especially in Greece and Italy.
"We urge the Government to act humanely and responsibly, and to maintain a positive commitment to the Dubs scheme within a comprehensive strategy to safeguard unaccompanied child refugees within Europe."
The letter is signed by Anne Longfield, Children's Commissioner for England, and Tam Baillie, Sally Holland and Koulla Yiasouma - her counterparts in Scotland, Wales and Northern Ireland respectively.
Yvette Cooper, Labour MP and chairwoman of the influential Home Affairs Select Committee, welcomed the intervention.
She said: "This is a very serious response from the children's commissioners. They make clear that far from avoiding traffickers, by ditching the Dubs scheme, the Government risks pushing more children back into the arms of smuggler gangs.
"The Government should listen to this call from the commissioners whose very purpose is to protect the welfare of vulnerable children and reopen the Dubs scheme now."
Ms Rudd has said the scheme is closing amid fears it is backfiring and encouraging child refugees to put their lives in the hands of people traffickers and make the perilous journey to Europe.
But critics say the opposite is true and ministers are leaving vulnerable children languishing in refugee camps at the mercy of traffickers.
The letter, which comes after interventions from the Archbishop of Canterbury, the Most Rev Justin Welby, and the head of the Catholic Church in England and Wales, Cardinal Vincent Nichols, piles further pressure on the Government to reverse its decision.
A legal challenge against ending the scheme is expected to reach the High Court in May.