Nearly 10,000 children aged five to seven are acting as unpaid carers for family members or guardians, according to figures that have been published which were described by one children's charity as the tip of the iceberg.

The data, compiled from the 2011 census, shows nearly a quarter of a million people under 19 in England and Wales were caring for parents, siblings and others – coping with pressures which charities say cause many to fall behind in school and miss out on their own childhoods.

An 80% increase in the number of five to seven-year-old carers in England over the last decade was one of the starker trends to emerge, although observers suggest this may be because the size of this group was under-reported in the past.

Girls are slightly more likely to be carers than boys, while youngsters from black, Asian or other minority ethnic communities were twice as likely to be carers. The Children's Society said that the figures were unlikely to represent the true picture as many child carers remain hidden from the view of authorities.

The charity called for greater state support for young carers, who it said were one and a half times more likely to have a long-standing illness or disability or special educational need than their peers. They also have significantly lower educational attainment at GCSE level – the equivalent of nine grades lower overall than their peers.

"Many young carers remain hidden from official sight for a host of reasons, including family loyalty, stigma, bullying, not knowing where to go for support," the charity said in a report, Hidden From View, which pointed out that the number of young carers in England had risen by a fifth since the last census in 2001.

The latest census figures reveal that a total of 177,918 minors are carers for their loved ones, with 15,728 providing more than 50 hours of care a week and 19,422 between 20 and 49 hours. Children aged 10–14 made up the largest group of young care providers, with 72,266 providing unpaid care.

Of the 9,985 five- to seven-year-olds providing care, 1,642 are doing so for more than 50 hours a week, and 1,166 for between 20 and 49 hours. In the eight- to nine-year-old age bracket, 12,148 children are giving care, 1,520 for more than 50 hours a week and 1,204 for between 20 and 49 hours. Statistics on the levels of health among child carers revealed that more than 2,400 had bad or very bad health, while more than 9,000 said it was "fair".

Matthew Reed, chief executive of the Children's Society, said: "This new figure is shocking enough, but we know from years of working with young carers that it is likely to be just the tip of the iceberg. Many often incredibly vulnerable young carers are slipping through the net, undetected by the support services they so desperately need."

David Holmes, chief executive of Family Action, which supports disadvantaged and socially isolated families, said it wanted the government to address the needs of young carers through the children and families bill currently before parliament. "We would like to see a duty on schools to identify young carers in the school population and the development of improved support," said Holmes, who added that many young carers felt unable to disclose their caring responsibilities because of a lack of trust in teachers or a fear of agencies intervening at home or worries about being bullied.

A Department for Education spokeswoman said: "We know young carers need more help and we are supporting local authorities to do much more for these dedicated young people. "We recently announced that young carers will be involved in the training of school nurses, so they know exactly what support they should offer and can champion their needs.

"We have also created a specific training guide for teachers to help them to better identify and support young carers – and funded the Children's Society and Carers Trust to support social services to adopt 'whole family' approaches to support young carers."

Case study: 'I had to grow up'

For Jack Garrigan, the moment he had to very quickly start taking on adult responsibilities came last year when his mother, Louise, lost her sight after the sudden onset of a rare virus.

"Mum was in hospital for a month and it was over four weeks that I had to grow up really," says the 15-year-old, who, along with his sister Laura, 10, is among nearly a quarter of a million children in England and Wales caring for a relative.

In the case of the Garrigan family, from the Blackley district of Manchester, it involves Jack stepping in to cook, shop and, in his mother's words, ensure the household keeps running.

"The three of us work as a team, so we all do our bit," he says. "On a typical morning for example my sister would help my mum get dressed and I would prepare the breakfast and make sure that Laura is looking nice for school too."

The routine takes its toll – "Sometimes you can get tired, especially when there are school exams going on as well" – and the he admits to missing some things that other 15-year-olds enjoy. "I used to go to a drama club workshop but I can't do it any longer because there is no way of getting there and I have too much to do," he says.

But he adds matter-of-factly: "At the end of the day she is my mum and whatever I do, I do it because I have to and because I want to."

Concerned that her son is playing down his role in the family, Mrs Garrigan adds: "I don't think he really knows how much he does because it's so constant and we are in a routine now. He does my tablets and prescriptions. He basically keeps the house going."

• This article was amended on 17 May 2013 to correct the spelling of Blackley, from Blakely.