Refugee children transferred from the Calais Jungle camp to areas across France have told of their desperation and pleaded to come to the UK urgently.
Some of those interviewed since being moved to reception centres following the dismantling of the camp said they did not feel safe in their new surroundings and were tempted to flee.
Just five of the 33 boys surveyed by Safe Passage for Citizens UK in the past week said they had been spoken to by Home Office officials since arriving at the centres.
The last children left the Jungle camp at the beginning of November, but fears are now growing for their welfare as they await information on their applications for asylum.
The charity has called on the Home Office to speed up the rate of transfers to the UK for unaccompanied children, and warned the temporary placements in reception centres should not be seen as a reason to delay bringing refugees to Britain.
Two children are already known to have fled the centres, the charity said, while three of the boys it spoke to reported being forced to work picking fruit.
Rabbi Janet Darley, Citizens UK Leader, said: "We are hugely concerned about the safeguarding of children in the CAOs (reception centres) in France. The Safe Passage team have had reports of forced labour, and unaccompanied children being made to live with adults.
"Although the CAOs are, on the whole, safe places for the children to live, they cannot be used as an excuse to delay the transfer of children to the UK. Every day children are separated from their families in the UK, or the opportunity to be placed with foster families, they are missing out on their childhoods."
One boy surveyed said he had "no proper food, clothes" and pleaded to come to the UK, while another said: "We are human not animals and we are stuck here".
Bishop Paul Butler of the charity said: "Children in France are getting increasingly desperate as they hear little from officials, and fill the void with rumours and speculation. With children already absconding from the CAOs it is vital that the Home Office speeds up the rate of transfers to the UK."
Earlier this week Home Office minister Robert Goodwill said the Government remains "absolutely committed" to bringing eligible children from France to the UK.
He said more than 300 children had been transferred from France since October 10.