A study of more than 15,500 three-year-olds has found that a higher proportion of family poverty exists in Wales than anywhere else in the UK.
University researchers described the survey results as "shocking"
The survey by the University of London found 30% of families in Wales were living below the poverty line.
This compared with 25% in England and 21% in Scotland.
The study also found children from disadvantaged families were educationally already up to a year behind others by the age of three.
The cognitive development, health and welfare of the toddlers between 2003 and 2005 was surveyed.
The study also revealed that obesity is a more significant problem in Wales than the rest of the UK, with almost one in every four three-year-olds being either overweight or obese.
Professor Heather Joshi, director of London University's Centre of Longitudinal Studies, said that the results were "shocking" and could have implications for the future.
"We have studied people throughout their lives before and the imprint of having lived in poverty in childhood can be traced through school and into adult life, so finding such a lot of disadvantage amongst a big minority of today's children is very disturbing," she added.
But she said it was possible for people to change their circumstances.
"You shouldn't abandon hope - a lot of people triumph against the odds, but then a lot of people don't," she said.
"There are some signs that if poor children get a place in a good preschool nursery that they do just as well as more privileged children getting good quality childcare.
"But this doesn't apply to all of them by any means."
The findings came just days after First Minister Rhodri Morgan unveiled his legislative programme which included moves to tackle childhood poverty and assist vulnerable children.
Meanwhile, Plaid Cymru AM Leanne Wood has called for a review of the Communities First project which was set up to help some of the most deprived areas in the country.
Research carried out by BBC Wales has found that over £6m of public money was sent back unused.
The Welsh Assembly Government has blamed short-term staff vacancies.