A full reversal of the cap, introduced by the Conservatives in 2017, is estimated to cost £3.6 billion and lift 630,000 children out of poverty.
The IFS also presented options for partial reversals, including exempting working families, which would cost £2.6 billion and reduce child poverty by 410,000.
Another partial option involves paying half the rate for third and subsequent children, costing approximately £1.8 billion.
A government spokesperson highlighted plans for an ambitious strategy from the Child Poverty Taskforce and investments such as £500 million for children's development and a £1 billion crisis support package.