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 75-year-old comic book character has been named UN ambassador for the empowerment of women and girls.
The women have gone straight to the top of the charts with their new song, Shout Out To My Ex.
The country reflects after the two main presidential candidates tore into each other at a usually-civil and light-hearted charity event.