The move came after French President Francois Hollande urged the UK government to assist in resolving the refugee crisis in Calais, also stressing the need to completely demolish the so-called Calais Jungle.
The letter, organized by the charity Citizens UK, was signed by former Archbishop of Canterbury Lord Williams, and several highly-placed British Muslim and Jewish leaders.
In the letter, they referred to the children who "have fled conflict and persecution, are now stuck in Northern France, deeply traumatized and at great risk, as well documented by the anti-slavery commissioner you yourself appointed while Home Secretary."
They said that "we are now just days away from the start of the full demolition of the Calais camp" and that "the time to act is now."
"None of us want the Calais 'Jungle' to exist. It is a stain on the conscience of both France and Britain," the letter inveighed.
Referring to the imminent demolition of the Calais camp, the religious leaders underscored "the paramount need" to protect children, recalling that "during the last such demolition, the charity Help Refugees documented that 129 children went missing."
Earlier this year, French President Francois Hollande pledged that the Calais Jungle would be shut down by the end of 2016.
The camp is notorious for its squalid conditions, the numerous attempts of its inhabitants to break into the Channel Tunnel in a desperate bid to reach the United Kingdom, and multiple police raids.
Meanwhile, a report by Medecins Sans Frontieres (MSF), or Doctors Without Borders, an international humanitarian organization, said that the demolition of the Calais camp will hit unaccompanied foreign minors and people with mental health problems especially hard.
"There are 861 unaccompanied foreign minors among the refugees currently living in Calais, 627 of them in the 'Jungle' itself. Mostly from Sudan, Afghanistan, Eritrea or Ethiopia, the youngest is only 10 years old," according to the report.