A shortage of graduate teachers working in the early years sector means many young children are at risk of falling behind before they start school, a charity warns.
Save the Children says there are nearly 11,000 too few early years teachers working in nurseries across England.
It says all children should be in childcare led by graduate early years professionals for the best start.
The government says the charity's claims are misleading.
Save the Children's warning comes a week after Education Secretary Damian Hinds said it was a "persistent scandal" that youngsters were starting school unable to communicate in full sentences or read simple words.
The charity analysed data obtained through Freedom of Information requests to the Department for Education.
It concludes that 10,731 nurseries, playgroups and children's centres - out of a total of 21,041 - do not have staff with qualified teacher status (QTS), early years teacher status (EYTS) or early years professional status (EYPS).
Tory MPs warn ministers over nursery funding
Four ways to get more men teaching kids
Nursery qualifications U-turn 'huge relief', say campaigners
Toddlers 'need early years teachers in nurseries'
QTS is typically held by school teachers, while EYTS and EYPS are broadly equivalent and focus specifically on early years education.
The charity estimates that this means that some 325,000 children are at early years facilities where there is not a staff member with one of these accreditations.
The charity fears a shortage of qualified teachers in early years settings will have a negative impact on children, particularly the more vulnerable.
"Children who start behind, stay behind," says Steven McIntosh, Save the Children's director of UK poverty.
"But high-quality childcare, led by graduate early years teachers, can ensure children are ready for school. So instead of lowering ambitions for childcare quality, the government should keep its promise to address the crisis in training, recruiting and retaining these underpaid and undervalued teachers.
"All of our little ones should have access to nursery care led by an early years teacher. Without action, we'll be letting down our next generation."
Mr McIntosh says addressing "this chronic shortage" of early years teachers should be at the forefront of Mr Hinds's ambition to improve social mobility.
