The Do it 4 Real scheme, run by the youth hostel organisation YHA, charges £49 for a place on one of its five-night summer camps for young people aged 10 to 19.
But children in care are exempt from the offer, instead having to foot the full £299 bill, more than six times the cheaper rate.
The Do it 4 Real website states: "The price of a place on camp for a looked-after child is the higher price. This is because all looked-after children have access to a range of alternative funding streams."
John Kemmis, chief executive of advocacy charity Voice, said the fees would particularly disadvantage children in foster or kinship care, whose families may not be able to afford the camp and do not have access to "alternative funding streams". "It's unfortunate they're discriminating against children in care," he said. "In the current economic climate they may find it very difficult to get money out of local authorities for this kind of thing."
Cathy Ashley, chief executive of charity Family Rights Group, said foster carers only receive money to cover the basic costs of raising a child. "The impact of this is that looked-after children are more likely to be excluded," she said.
Janet Rich, trustee of the Care Leavers' Foundation, described the move as "thoughtless", adding: "It would be nice if by way of apology they could offer half-term camps for looked-after children free of charge."
A Department for Education spokeswoman said while a pricing structure had been agreed with the charity, the organisation was free to devise promotional offers.
A spokeswoman for YHA said that money is available to social workers and carers of looked-after children through funds including the Personal Education Allowances. But added: "When a social worker or carer, unable to access funding, contacts us, we consider each case on an individual basis."
So far 677 applications have been received from looked-after children this year.
