The former Archbishop of Canterbury is putting his name to a letter in The Times newspaper on Tuesday, reminding the government of the "urgency of the situation."
The note has also been signed by the Bishop of Barking, Rt Revd Peter Hill, and senior Rabbi Laura Janner, among 30 others.
It calls on David Cameron to make sure all child refugees at Calais with just grounds to be in the UK are here by September.
The signatories are urging that the first 300 youngsters in Greece and Italy identified as most vulnerable should be the first to come over.
They warn "ten thousand refugees have gone missing in Europe", while even those with entitled to be reunited with relatives in Britain have often "been stuck in limbo for months."
The letter welcomes an announcement made last by the government that it would bring vulnerable refugee children from Europe to the UK.
It says "Our respective communities stand ready and willing to help".
The letter adds: "Citizens UK has identified 157 children in Calais with family in Britain who will spend tonight in the mud and danger of "The Jungle" [in Calais].
"Conditions in Greece are appealing, with widespread reports of children living destitute in the street."