Britain risks "sleepwalking into a world where inequality becomes so entrenched that our children grow up in a state of social apartheid", according to a leading charity.

In a damning report to be published next week, the National Children's Bureau finds that, in many respects, child poverty is now a bigger problem than during the 1960s, when it carried out a seminal study, Born to Fail?.

The report compares aspects of children's lives today to data from the Born to Fail? cohort study of 11-year-olds, carried out in 1969. It finds that significantly more children are growing up in relative poverty today – 3.6 million compared with 2 million – and claims that these children suffer "devastating consequences throughout their lives".

It adds: "Today, although there have been some improvements, overall the situation appears to be no better, and in some respects has got worse."

The report finds that:

■ A child from a disadvantaged background is still far less likely to achieve a good level of development at four than a child from a more privileged home.

■ Children living in deprived areas are much more likely to be the victim of an unintentional injury or accident in the home.

■ Children from the poorest areas are nine times less likely than those living in affluent areas to have access to green space, places to play and to live in environments with better air quality.

■ Boys living in deprived areas are three times more likely to be obese than boys growing up in affluent areas, and girls are twice as likely.

"Our analysis shows that, despite some improvements, the inequality and disadvantage suffered by poorer children 50 years ago still persists today," said Dr Hilary Emery, the bureau's chief executive.

"There is a real risk that our society is sleepwalking into a world where children grow up in a state of social apartheid, with poor children destined to experience hardship and disadvantage just by accident of birth, and their more affluent peers unaware of their existence."

The report warns that Britain could become a place in which "children's lives are so polarised that rich and poor live in separate, parallel worlds".

It draws comparisons with other developed nations and claims that a lack of ambition causes children in the UK to suffer unnecessarily. As a result, patterns of disadvantage could become permanent features of our society.

The charity claims that, if the UK emulated the example of those European countries deemed to be the best places to grow up in, the deaths of 172 children through unintentional injuries alone could be prevented every year, 320,000 more 15- to 19-year-olds would be in education or training, and nearly 45,000 fewer 11-year-olds would be obese.

Both the previous and current governments have made tackling child poverty a key commitment. There has also been an emerging consensus among politicians that more needs to be done to help working parents in order to lift families out of poverty.

The report's authors praise the strides made in improving young children's access to nurseries and playgroups. But they note that the majority of children growing up in poverty – 63% – have at least one parent or carer who is in work.

The charity is calling for urgent action from the government to address the poverty and disadvantage that it claims "still wreaks havoc on children's lives, causing them to lag far behind their more affluent peers in almost all areas of their lives, from health to education, early development to housing".

The report also notes: "The government made a commitment to protect pensioner benefits but there has been no equivalent commitment to protect children living in the poorest families or to tackle child poverty."

There are concerns that changes to the benefits system will see ever-greater numbers of children fall into poverty in the coming years, further threatening the UK's goals of significantly reducing the problem by 2020.

The co-author of the original Born to Fail? report said that the fact that so little had changed showed a failure of political will.

"You are always going to get people saying we will always have poor people," said Peter Wedge, emeritus professor at the University of East Anglia.

"That cannot be denied. But it is the gap between that is important. It is about what happens to those who have resources and those who don't. We can change that as a society if we have the will."