CashSYDNEY - A New South Wales Government proposal to introduce fees in public school preschools will hurt children from struggling families and set them up for a life of disadvantage, the Greens have warned.

More than 60 principals, teachers and parents will attend a forum in Parliament House on Wednesday afternoon about the plan to introduce the fees from next year.

Greens MP John Kaye said the proposal demonstrated "a singular lack of understanding of public education", and sacrificed educational outcomes for a boost to the budget's bottom line.

It also risked stigmatising children on the basis of their family background, he added. "Compulsory fees are not only a deterrent to entry for low socio-economic background families, but an insult to the notion of free, secular and comprehensive (education).

"The benefits of preschool are well established in Australian and international studies ... fees put at risk improvements to lifelong learning outcomes, social adjustment to school life, long-term further engagement in education and income levels."

Kaye said the proposal would result in the government spending more on health and criminal justice. Speakers at the forum include NSW Education Minister Adrian Piccoli, opposition education spokeswoman Carmel Tebbutt and Dr Kaye.