Free childcare should extend to all pre-school children or those missing out will fall behind, a report says.
The Welsh Government has promised 30 free hours a week for three and four year olds with working parents.
But children's commissioner, Prof Sally Holland, says in her annual report children of unemployed parents will fall behind their peers if they miss out on this service.
The Welsh government promised to study her report "in due course".
By the age of three, children from the poorest backgrounds are about 10 months behind those from better-off families in terms of development, according to the Millennium Cohort Study.
The commissioner believes making sure all children receive the same care will reduce this gap.
She said: "There is clear evidence that if you invest in early years' education and high quality childcare it makes a significant difference to the life chances of children from the poorest backgrounds and promotes social mobility."
She said she wants to avoid a situation where children of non-working parents miss out and are denied a chance to reach their full potential.
The report calls for other changes, including a register of children being educated at home, help for adopted children to contact siblings and help for parents to communicate more easily with deaf children.
A Welsh Government spokesman said: "Work is the best route out of poverty, and the greatest protection against it.
"Our childcare offer is designed to remove a major barrier to work and tackle in-work poverty by reducing the costs of going to work.
"Other Welsh government schemes, such as PaCE, are designed to help parents cover the costs of childcare while they gain the skills and experience to find work."
-reprinted from BBC News