Families whose children get free school meals should get top-up payments to help feed them during the summer, Plaid Cymru's Steffan Lewis has said.
The AM called for the Welsh Government to be given powers to top-up Department of Work and Pensions benefits.
It follows a cross-party report which warned the loss of free meals during school holidays can heighten the risk of hunger among children.
The UK government said it was helping millions meet the cost of living.
Currently, more than 76,000 children in Wales are eligible for free school meals.
The UK-wide All-Party Parliamentary Inquiry into Hunger in the United Kingdom in April said hunger among children during school holidays "is one of Britain's hidden costs of poverty".
Survey data seen by the inquiry found a "significant proportion of teachers and school staff notice children returning to school hungry on the first day after the holidays".
The report called for councils to be given an obligation to facilitate the delivery of free school meals during term time and for funding to be allocated from the sugar tax.
But Mr Lewis, Plaid spokesman for non-devolved matters, argued powers should be devolved so the Welsh Government can provide extra cash to families who have free school meals over the holidays.
The benefits system in the UK is not devolved and is the responsibility of the UK government.
"It is estimated that the loss of free school meals during the break can add £30 to £40 a week to parent's outgoings," said Mr Lewis.
"For those who are already on the breadline, summer holidays can be the final straw.
"We should be supporting them to ensure that they have access to plenty of nutritious food over the summer break."
"We live in one of the wealthiest countries in the world, yet teachers report that children are returning from school holidays malnourished," Mr Lewis added.
In Wales there was a 10% increase in the number of three day emergency food supplies given to children in July and August 2016 compared to the previous two months, according to figures from the Trussell Trust.
A total of 5,185 three-day emergency food supplies were provided for children by The Trussell Trust's food bank network in Wales during July and August 2016, compared to 4,733 in May and June 2016.
One Swansea food bank launched an appeal in July after it ran out of supplies, saying the end of the school year saw families struggle without free dinners provided.
A UK government spokeswoman said: "Through the Wales Act 2017 the UK government is putting in place a clearer, stronger devolution settlement for Wales, with a clear boundary between devolved and reserved responsibilities.
"We're helping millions of families meet the everyday cost of living and keep more of what they earn. We are helping parents with the cost of childcare through our tax free childcare scheme."
A Welsh Government spokesman said: "We are already investing £500,000 to help provide quality meals and fun educational activities during the school summer holidays to help pupils from some of Wales' most deprived communities.
"The money will help provide breakfast, lunch, education about eating healthily and a programme of activities developed through schools taking part."