Handing down her interim report on Monday, former prime minister Julia Gillard delivered 33 recommendations, urging SA to take the lead in early education through a program to begin in 2026 and be fully implemented by 2032.
Australian Education Union federal president Correna Haythorpe said Ms Gillard's findings had national significance.
"The expansion of universal preschool for all three-year-olds in the state will deliver benefits that flow across a lifetime for South Australian children and their families," she said.
"With access to universal preschool for all three-year-olds, all families in South Australia can ensure that their children are meeting their developmental milestones, regardless of their financial conditions or socio-economic background."
Ms Gillard called for three-year-olds to be provided with 15 hours of preschool for 40 weeks a year, similar to what is offered to four-year-olds.
That could be through government schools and also through private early learning centres and long daycare facilities, depending on the model adopted.
"I do believe that as a caring state, South Australians feel that we have a moral obligation to make sure every child has the best opportunity, to grow and learn and thrive," Ms Gillard said.
"The research tells us crystal clear that intervention in the early years can make the biggest difference."
Ms Gillard's report found that up to 11,130 new preschool places would need to be created at a capital cost of up to $139 million.
Extra ongoing funding to support the system once fully operational was put at between $121m and $357m, with between 1497 and 2180 more staff needed in form of teachers, educators and directors.
Ms Gillard said her review contemplated extra preschool hours being provided to children most at risk of developmental delays, following evidence that without early intervention they would find it difficult to catch up.
"That disadvantage will continue to show in their adult life," she said.
"It shows in life expectancy, in poorer health, in poorer economic outcomes, in greater welfare dependency and even in involvement with crime."
Premier Peter Malinauskas said Ms Gillard's report had the power to change lives, describing a number of its recommendations as ambitious, with a key challenge delivering the necessary workforce.
"But that's exactly what we wanted. The whole idea of having the royal commission was to give us a clear roadmap to tell us what we need to do and by when," he said.
The premier said the government fully understood the program would be expensive.
"This isn't something we're going to squib. We believe it's worthy of that investment," he said.
"I don't think it's a question of can we afford to do this. I think it's a question of can we afford not to do this."
Former SA premier Jay Weatherill, who now heads up the Minderoo Foundation's Thrive by Five initiative, said the report's recommendations were the kind of bold reforms South Australia needed to ensure high-quality early learning and care was truly accessible and affordable.
"Having the option to access free early childhood education will benefit many children by positively impacting their social, physical, mental and emotional wellbeing, and setting them up for their lifelong learning journey," Mr Weatherill said.
Ms Gillard is due to hand down her final report in August.
