Older claimants and bereaved parents with young children will receive less money overall, experts warned.
Cohabiting couples will get nothing even if they have children, despite the rising number of unmarried people living together.
Previously, claimants got around £29,000 over a “support period” of up to 20 years, while those with very young children could claim even larger total sums.
However, from April 6 the Bereavement Support Payment will help for 18 months, with a maximum payout of just £9,800.
The widowed partner will receive a tax-free lump sum of £2,500, or £3,500 if they have dependent children.
They will then receive a monthly tax-free payment of £100 for 18 months, or £350 if they have children. Simon McCulloch, director at CompareTheMarket.com, said bereaved families with young children previously received support until the youngest child left school.
“The new payment could amount to a cut of £31,000 for the lowest income families and more than £12,000 for the average working widowed parent,” he said.
Johnny Timpson, protection specialist at Scottish Widows, said the reforms have also failed to keep up with social changes because benefits are only for those who lose a spouse or civil partner.
“It seems harsh to deprive children of financial support following a parent’s death based on their parents’ marital status,” he said.