The government's Sure Start programme is failing to support black and minority ethnic groups, says a review.
Sure Start was set up to support pre-school-age children
This was the finding of a university evaluation of the flagship scheme to help families with young children.
The study said Sure Start risked being a "missed opportunity" in terms of helping marginalised minority groups.
It said this was "very serious criticism", when social indicators showed these were the very groups most needing to benefit from the scheme.
Sure Start local programmes (SSLPs) are part of a multi-billlion pound initiative to tackle child poverty and support families in poorer areas.
The evaluation, led by the University of Hull, found some local programmes had abandoned attempts to form links with certain minority groups, "effectively excluding some already very marginalised communities".
Many local services showed poor practice in terms of translation and interpretation.
The review also raised concerns about the paucity of black or ethnic minority staff employed in senior positions in SSLPs, saying this raised a "negative message within and outside the projects".
The report said: "Too often SSLPs took a whole population approach when social and economic indicators suggested that they should be targeting specific minority communities.
"Although some programmes had an effective structural approach to minority groups, the majority were tending to respond in an ad-hoc, short-term way and often did not reach families who needed help.
"This was particularly true of groups described as 'hard-to-reach': very small populations, groups of travellers/gypsies/Roma, migrant workers, families of Bangladeshi origin."
It said that where Sure Start programmes had been successful in this area, it was often after a "long period of challenging, slow and costly work".
'More we need to do'
The Minister for Children, Families and Young People, Beverley Hughes, said the report showed the benefits for children and families of having "different agencies working together under one roof".
She added: "There is still more we need to do - especially in terms of using effective outreach to engage with the most vulnerable and disadvantaged children and that is why we have introduced a new requirement for every centre to run a home visiting and outreach programme for the parents of all new babies."
In December the National Audit Office (NAO) published a report saying Sure Start children's centres must do more to reach out to the neediest families.
The NAO found that fewer than a third of the 200 Sure Start centres it investigated were making efforts to reach the most vulnerable.
It also said while families valued the scheme, it was hard to measure whether the government's £3.2bn investment was good value.