This would remove the current requirement for low-income families to apply and ensure all eligible children benefit, according to the House of Commons education committee.
Experts told the committee that language barriers and difficulty with the administration process are preventing some children receiving free schools meals, with one in 10 eligible pupils currently missing out.
“Failing to legislate for auto-enrolment would be a missed opportunity to feed hungry children at school,” said the committee.
It added: “We consider that the arguments for auto-enrolment in free school meals for those children currently eligible are conclusive.
“In the interests of alleviating hunger in schools and improving health and educational outcomes for the poorest children, auto-enrolment must be brought in without delay."
Its chair Helen Hayes has now tabled an amendment to the bill to reflect the committee’s recommendation.
She says she is also concerned over the lack of time MPs have been given to scrutinise the bill.
“While we welcome the government’s ambition in this Bill, my colleagues and I from across the political parties were disappointed by how the government has rushed this Bill through the House of Commons at the expense of time for proper scrutiny,” she said.
“With such wide-ranging reforms that will have dramatic, lasting consequences for children and families.”
She added that the Department for Education’s “need for speed should not have been prioritised over diligent examination of evidence”.
A report by the Fix Our Food campaign last October found that 200,000 eligible children in England are missing out on free school meals.
An auto-enrolment trial among 20 councils run by the campaign, which involves academics at the universities of Leeds, Cranfield, York and Oxford, led to 20,000 more pupils receiving the benefit.
Newcastle City Council became the latest council to automatically enrol pupils last December.
Hayes has also tabled amendments to the Bill around other recommendations made by the committee, including ensuring its plans to provide universal free breakfast clubs consider children with special educational needs and disabilities (SEND) by ensuring their home-to-school transport arrives in time.
A "national care offer" is also needed to avoid regional differences in the quality of support for those leaving care. Help with university accommodation from personal advisors and with transport costs to get to work or education need to be included in this. Hayes also wants to see care leaver only apprenticeships widely available.
Ministers are also asked to strengthen the requirement for children in care to receive mental health assessments. Too often these do not take place, warns the education committee.
