Kate Bell, from the Child Poverty Action Group, said rising rent costs in London would mean the benefit cap hits families in the capital extra hard.
"We don't think it's fair to make children suffer for this cap.
"The real reason why people are going to be hit by the cap is because of the cost of their housing - most of the money these people are receiving in state support is going to housing benefit, which, of course, goes to the landlord, not to the family."
More top news
The contract that set the Beatles on their way to superstardom is to go up for sale for the first time, and could fetch as much as £500,000.
The shortest man ever to have been measured has died aged 75, Guinness World Records has announced.
Britons have stepped forward to offer help to refugees after a photo of a drowned three-year-old boy prompted an outpouring of support.