Research undertaken by the children's charity shows 48 per cent of children in childcare settings do not have access to a qualified early years teacher or equivalent.
The charity has calculated that this is putting 325,000 children at risk of starting school behind in their education because its own research suggests children in early years settings without graduate-level teacher are almost 10 per cent less likely to reach their expected development levels by the time they go to school.
"Children who start behind, stay behind," said Steve McIntosh, director of UK poverty at Save the Children.
"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."
He added that "without action, we'll be letting down our next generation".
The regions with the highest rates of children without access to an early years teacher are the East Midlands, East of England (both 55 per cent) and the West Midlands (50 per cent). The North East has the lowest rate of children without access to an early years teacher (38 per cent).
Local authorities with the highest rates of children without access to an early years teacher are: Shropshire (82 per cent), Swindon (78 per cent) and Rotherham (72 per cent). Sunderland, Kensington and Chelsea, and Islington are the councils with the lowest rates of children without access to an early years teacher.
The charity has received backing from the National Association of Head Teachers, Ark academies and the National Day Nurseries Association, but the Pre-school Learning Alliance and the Department for Education have challenged its focus on graduate childcare workers.
"It's vital that, in looking for ways to improve quality across early education, we do not reduce a complex issue to a simple solution and a call for higher qualifications," said Neil Leitch, Alliance chief executive.
"Parents, and providers who do not employ degree-level staff, know quality is about more than staff's academic achievements - and that a degree is not the sole marker of the experience, passion and in-depth knowledge high-quality practitioners need."
Children's minister Nadhim Zahawi said: "Save the Children's claim is misleading; university study is just one route into the early years workforce. There are over 250,000 dedicated professionals in the private or voluntary early years workforce, with many coming from apprenticeship or on-the-job training routes.
"The quality of early years childcare has risen since 2010 with 94 per cent of providers rated 'good' or 'outstanding'."
In February 2017, Save the Children made a similar call for more graduate-level childcare workers after calculating that up to 800,000 children will start school behind their peers in literacy and numeracy due to the shortage of early years teachers.
According to a report published in April, just 595 people enrolled on courses that lead to early years teacher status in autumn 2017. In comparison more than 2,300 people signed up for these courses when they were first introduced in 2013.
Save the Children's latest figures are based on data obtained via Freedom of Information requests to the Department for Education.