Statistics published by the Department for Education show that that 216,384 eligibility codes for 30 hours childcare were issued by 31 August for children aged three.
Of which 152,829 or 71 per cent, were validated by 5 September. This leaves 29 per cent whose code has yet to be verified by a childcare provider or local authority. Without a validated code, parents cannot access free childcare.
It is not clear why the codes are yet to be verified - reasons could include parents having yet to approach providers, problems with the verification system, or local authorities and providers being slow at doing the verification.
Earlier in the year there were reports of parents struggling to register for the 30 hours scheme due to technical glitches.
Purnima Tanuku, chief executive of National Day Nurseries Association, said: "There appears to be a big gap between those eligible and those who have had their codes validated.
"The Department for Education estimated that 390,000 parents would be eligible for 30 hours funded childcare, but so far only 216,000 have had their codes issued and only 71 per cent of those have had them validated.
"Those parents who could not access their codes by the end of August will now have to wait until January, missing several months of funded childcare. We know that some parents were given manual codes, but we don't know exactly how many yet.
"Also if their child starts later this month, will the government funding be backdated for providers and will this cause a further delay in the money being available to them?
"There must be a very clear and urgent communication for both providers and parents on this issue."
A DfE spokesperson said: "We are spending over £2.5bn on 15 hours of free childcare for disadvantaged two-year-olds over five years. We know that the take-up of this offer is rising, with 71 per cent of disadvantaged two-year-olds accessing a place - an increase of 13 percentage points since 2015."
As of 1 September, working parents in England are entitled to 30 hours of free childcare for three- and four-year-olds, up from the previous 15 hours.