The inappropriate use of Internet by kids in mobile phones leave their parents powerless to stop the access, says study.
Parents are also worried that internet-ready mobile phones leave their offspring open to direct and inappropriate advertising.
The fears were revealed by the new review currently being carried out by the charity Mothers' Union for the children's minister Sarah Teather, reports the Telegraph.
The study found that nine out of 10 parents now think that their children are growing up too quickly because of increasing sexualisation and commercial pressures, mainly from the Internet and television.
It has discovered that direct advertising through mobile phones was the marketing tool that most angered parents - with more 35 percent believing it was totally wrong.
This was followed by products-linked to social networking websites, which invite the children to click to "like".
The review, conducted by Reg Bailey, chief executive of the Christian charity, has also uncovered growing concerns about the exposure of children to sex on television.
In a poll of 1,000 parents conducted for the review, 41 percent of parents said that in the previous three months they had seen television programmes or advertisements before the 9pm watershed that they considered wrong for their children to view because of their sexual content.
In addition, 40 percent said they had seen window displays or advertising hoardings that children should not be exposed to.