At least 64 children are sexually abused every day in England and Wales, figures obtained by the NSPCC suggest.
More than 23,000 offences - including rape, incest and gross indecency - were recorded by police in 2009-10, an 8% increase on 2008-9, the charity said.
For the first time, its research also looked at the age of abusers and found a quarter were aged under 18. One in four victims was aged 11 or under.
The Home Office said the figures were "appalling".
The figures for recorded sex crimes against children were obtained through a successful NSPCC freedom of information request to all 43 police forces in England and Wales.
The figures showed that more than half of the victims were aged between 12 and 15, one in four was aged five to 11, and more than 1,000 were aged four or younger.
Girls were more than six times more likely to be assaulted than boys, with 86% of attacks taking place against females, the figures showed.
The police force reporting the largest number of crimes was London's Metropolitan (3,672), followed by West Midlands (1,531) and West Yorkshire (1,205).
Jon Brown, who heads the NSPCC's work on child sex abuse, said the increase was a "real concern".
"Thousands of people come forward every year to report sex crimes against children. But many victims are too young to ask for help. Others are too scared to tell anyone about their suffering until years later," he said.
"More than 2,000 suspects in these cases were under 18. It's clear we need more services that address the harmful sexual behaviour of young people, as well as adult offenders."
The Association of Chief Police Officers (Acpo) warned that recorded crime figures were "not a good indicator of the prevalence or trends of child sexual abuse" as much abuse went unreported and rises could be attributable to victims of historic abuse coming forward.
However, Assistant Chief Constable Peter Davies, the Acpo lead for child protection and child abuse investigation, said: "Understanding the crime though is central to success.
"We are starting to bring it out of the dark places where victims suffer in silence for fear of reporting while recent infiltration of intricate global paedophile networks is further testament to the work we have collectively done to understand how offenders think and operate."
A Home Office spokesman said the government would continue to work with groups like the NSPCC to protect the most vulnerable people in our society.
It pointed to the roll-out of the child sex offender disclosure scheme across police forces in England and Wales earlier this year.
This allows parents to check whether someone in contact with their child is a convicted sex offender.
Dubbed "Sarah's Law", it was proposed after the murder of eight-year-old Sarah Payne by a convicted sex offender, Roy Whiting, in West Sussex in 2000.
The Home Office said this was a "major step forward in our ability to protect children from sex offenders".