In a joint statement, the UK's Children's Commissioners, including Scotland's Commissioner for Children and Young People Tam Baillie, said they were concerned by the "serious negative impact" the proposals would have on children.
They said: "We urge the UK Government to reconsider its plans, specifically the £26,000 benefit cap to be imposed on families each year."
They argue the cap is likely to lead to more families becoming homeless and breach UN child rights rules.