Childhood is over for many children by the age of 12, according to members of a parenting website.
Netmums website users are complaining that children are under pressure to grow up too fast.
They say that girls are made to worry about their appearance and boys are pushed into "macho" behaviour at too young an age.
The website's co-founder Siobhan Freegard blamed a "toxic combination of marketing, media and peer pressure".
"The pace of modern life is so fast that it is even snatching away the precious years of childhood," she said.
"Children no longer want to be seen as children, even when as parents we know they still are."
"There needs to be a radical rethink in society to revalue childhood and protect it as a precious time - not time to put pressure on children to grow up far too fast," said Ms Freegard.
The website asked for its members' views and received more than a thousand replies.
The most common view - from more than two-thirds of this group - was that childhood was now over by the age of 12.
About a third of those replying to this online snapshot believed that childhood ended even sooner, at the age of 10.
Parents voiced concerns that children were being put under pressure to act older than their years.
Girls were made to worry about their appearance and their weight, boys were meant to act tough and both boys and girls were under pressure to take an interest in sex at too young an age.
"Children need time to grow and emotionally mature in order to cope with what life throws at them," says Ms Freegard.
This is the latest example of parental concerns about children growing up in an oversexualised culture.
Claire Perry MP, the prime minister's adviser on childhood, has warned about children accessing inappropriate material on websites or through mobile phones.
Another MP, Diane Abbott, attacked what she called the "pornification" of youth culture, in which young people were growing up in an environment of sexual bullying and explicit sexual images.