Free childcare should be offered to unemployed parents on courses or training linked to finding work, a report by assembly members has said.
A limited trial offers working parents 30 hours a week of free childcare.
Restricting it to working parents risked increasing the gap in attainment between the well-off and less well-off, the children's committee said.
The Welsh Government said it had projects helping with childcare costs for parents looking for work.
The scheme offering free childcare for parents of three and four-year-olds is currently being piloted within seven council areas with a plan to extend it to the whole of Wales by 2020 at an estimated cost of £100m a year.
The report published on Wednesday into the general principles of the Childcare Funding (Wales) Bill said lessons should be learned from the pilot schemes.
Committee chair Lynne Neagle, a Labour AM, said: "We welcome the steps taken by the Welsh Government to legislate to make it easier for parents to apply for the childcare offer.
"However, we are concerned about the extent to which the proposed national childcare offer, facilitated by this Bill and being piloted in different areas of Wales at the moment, targets those most in need of support."
She added: "We agree with the Welsh Government that creating a national eligibility checking system, to be administered by HMRC, should make it more straight forward for parents to apply, and ease the administrative burden on local authorities."
"However, we are concerned that restricting the bill's provisions to the children of working parents risks increasing the gap that already exists between our most disadvantaged and advantaged children in terms of their development and educational attainment.
"For this reason, we recommend that the Bill be amended to extend its provisions beyond working parents, to include parents who are seeking work by undertaking education and training linked to securing employment."
The committee also suggested reviewing the target age group, saying the Welsh Government's own national survey found demand for childcare to be highest for children aged one to three.
Despite the criticism, seven of the eight committee members said the assembly should still agree the general principles of the bill.
Plaid Cymru's Llyr Gruffydd refused to sign up, because his party says that restricting the funding to parents who are in work puts the poorest families at a disadvantage.
"If they get away with it, they'll be making the attainment gap between the poorest and better off children into a yawning chasm," he said.
On Friday, Minister for Children Huw Irranca-Davies announced a £60m fund to build and refurbish nurseries, amid concerns that some parents were not taking up the offer because the care was not available in a convenient place.
A Welsh Government spokesman said: "We note the committee's report and will be considering its recommendations.
"However, we are clear that the government's commitment is to develop a childcare offer that helps parents into or return to work. It aims to remove an acknowledged barrier to employment and free up money that they can use to improve their family's circumstances.
"It is also important to remember this is one of a suite of programmes aimed at supporting parents with the costs of childcare," he added, pointing to projects including Flying Start and an EU-funded programme to support parents returning to work.