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
Half of those killed or maimed in the last 72 hours of intense bombardments in Aleppo have been children.
Astronomers said: "Europa’s ocean is considered to be one of the most promising places that could potentially harbor life".
The rain will ease in the west tonight, but the cloud cover will remain across much of England, Wales and N. Ireland.