Doctors and nurses have piled pressure on the Tories to immediately offer free school meals to thousands more needy children.
Groups representing hundreds of thousands of medics said all pupils from Universal Credit families in England must get free dinners "as a first step to universal provision".
The Royal College of Paediatrics and Children Health, British Medical Association and Royal College of Nurses are among the signatories to a letter to Chancellor Jeremy Hunt and Education Secretary Gillian Keegan demanding urgent action to prevent kids going hungry.
“Every day, healthcare professionals see the impact of hunger and malnutrition in their work,” say the group that also includes TV medics Dr Adam Kay, Dr Alex George and Dr Chris van Tulleken.
"The Government’s free school meal scheme has been shown to be an effective policy solution to reduce obesity, food insecurity and health inequalities," the letter said.
"However, currently 800,000 children living in poverty do not qualify for this nutritional safety net due to the criteria being too low.
"For many of these children, they may have to skip lunch completely or rely on cheap, unhealthy food that is damaging to their long-term health."
The Mirror and the National Education Union are campaigning for all primary school pupils in England to get free school meals, in line with promises in Scotland and Wales.
All young children in England can get free school meals up to the end of Year 2 but after that it only applies to households on certain benefits.
Children living in Universal Credit families can only get the benefit if their parents earn less than £7,400-a-year from work.
Spiralling cost of living pressures have fuelled calls for the scheme to be expanded to all Universal Credit families, which is being backed by TV chef Jamie OIiver and the Government's former food tsar Henry Dimbleby.
The move would offer free lunches to around 1.4 million additional children and would cost an estimated £500 million a year.
The latest food insecurity data revealed that more than 4 million children live in homes without proper access to food, risking their health and their life chances.
The analysis for the Food Foundation found that one in four (26%) of households with kids reported skipping meals, eating less, or going hungry all day in September.
The problem has deepened since April, when 2.6 million children lived in homes where they struggled to get enough to eat.
Professor David Strain, chair of the BMA board of science, said: "With the cost of living rising, more and more children are threatened with food poverty, which can mean more malnutrition and more obesity as families turn to cheaper and less healthy options."
He went on: "The new Prime Minister has said he won’t leave the next generation ‘with debts to settle that we are too weak to pay ourselves’.
"Refusing to extend free school meals would leave a health debt that doctors will be dealing with for years to come."
Dr Helen Stewart, of the Royal College of Paediatrics and Child Health, said: "We are seeing the impacts of poor nutrition every day, with both poor growth of deprived babies and children on the one hand, and rising child obesity on the other.
"Teachers are telling us about seeing hungry children in school and the impact on their wellbeing and learning. Many parents have no option but to buy cheaper lower quality and less nutritious food in order to feed their children and pay their bills.
"I believe we have a moral responsibility to help these families and to ensure that all children have enough to eat."
It comes as the boss of supermarket chain Iceland said extending the scheme was a "critical priority".
Richard Walker, who is standing to be a Tory MP, said: "Food insecurity is inevitably on the rise, and it’s the households with kids who are most at risk."
He added: “If our country is to succeed long term, we have got to make sure we have a healthy, focused happy, engaged school population who have decent prospects, and that has to include vulnerable kids."
A Government spokesperson said: “We have expanded access to free school meals more than any other government in recent decades, which currently reach 1.9 million children. We are also investing up to £24m in our National School Breakfast Programme, which provides free breakfasts to children in schools in disadvantaged areas.
“In addition, eight million of the most vulnerable households will get at least £1,200 of cost-of-living support this year on top of benefit from the Energy Price Guarantee - meaning they will be eligible for support which exceeds the average rise in energy bills by hundreds of pounds.”
