Almost 8,000 sex offenders have been cautioned across England in the past five years, rather than being charged.
Offences involving children accounted for more than 1,600 of the cautions, while more than 240 were for rape.
The Association of Chief Police Officers (Acpo) said a caution would be given only if it was the most appropriate course of action.
The government said there were very few cases where cautions were appropriate for rape or offences against children.
'Very careful thought'
Acpo said a caution did not mean the offender was being "let off" as it still brought a criminal record and a caution for a sex crime would also see the offender placed on the sex offenders register.
The results were revealed after inquiries to every police force in England by the BBC News website, many of them made using the Freedom of Information Act.
Every force provided figures except West Yorkshire Police, which said it would be too expensive to search for the results.
Crimes dealt with by a caution included offences as varied as rape, downloading child porn, bigamy, exploitation of prostitution, indecent exposure, sexual offences against animals, sexual grooming and familial sex offences (incest).
Of the offences against children dealt with by a caution, more than 350 were cases involving a victim aged under 13.
Terrence Grange, Acpo lead for sexual offences and Chief Constable of Dyfed Powys Police, said: "Every decision made to prosecute or issue a caution is reached after very careful thought and consideration.
"Every incident will be treated on its own merit, taking into account the circumstances of the incident and the people involved.
"A caution will only be given if it is agreed to be the most appropriate course of action. These decisions are usually taken after full consultation with our partners."
Admission of guilt
Acpo said the age, welfare, mental well-being and views of the victim would be taken into account as would the severity of an attack.
It said circumstances where a caution would be given for rape could include cases where the victim does not turn up to give evidence in court.
An admission of guilt is needed for a caution.
Admitting guilt means being put on the sex offenders register.
The caution will show up on a search of criminal records.
The CPS decides how to handle rape cases.
The CPS says cautions are only used in exceptional cases.
Rape carries a maximum life sentence.
Acpo also said cautions were likely to be given in cases where, for example, a 16-year-old boy had consensual sex with his 15-year-old girlfriend, who may be in the same class at school as him.
This would be a criminal offence - unlawful sexual intercourse with a girl under 16 - but would usually not be pursued through the courts.
But it said in any situation there would have to be a clear admission of guilt. It left the offender with a criminal record and - in the case of a sex offence - the need to go on the sex offenders register.
A spokesperson for the Ministry of Justice said: "The government is committed to securing more convictions in rape cases and has commissioned the child sex offender review to ensure that children are better protected from paedophiles.
"There are very few circumstances indeed where a caution for rape or offences against children is the most appropriate sanction.
"Use of cautions is a matter for the police but in exceptional circumstances - for instance where the victim does not want to proceed with a prosecution."
Women Against Rape said cautions felt like a setback for victims
The Conservatives and Liberal Democrats both said the number of sex offenders being cautioned was far too high - and blamed the policies of the government.
Shadow Home Secretary, David Davis, said: "It is bad enough that so many offenders are getting away with effectively no punishment. It is outrageous that this is happening in very serious cases of sexual assault involving children.
"This is a direct consequence of Labour pursuing a policy of getting detections by the easiest possible route even if it means keeping thousands of serious offenders out of the justice system.
"The appalling effect it has on public safety of some of the most vulnerable in our country is something Labour should be truly ashamed of."
Nick Clegg, the Liberal Democrat spokesman on home affairs, said: "There are many circumstances in which the police rightly use cautions, but the public will be shocked to learn that it is taking place on such a large scale for such serious offences.
"This is part and parcel of a wider trend pushed by Tony Blair for the police to bypass traditional justice in favour of fixed penalty notices and other measures outside the courts.
"There is also alarming evidence that these shortcuts to justice are being used in increasing numbers so that the police can meet the rigid and arbitrary targets imposed by this government.
"We need urgent clarification whether this is the result of the perverse pressure placed upon the police by government targets."
The campaign group Women Against Rape said: "It takes an enormous effort for a traumatised woman who has been sexually assaulted to come forward.
"It is a slap in the face when the man is let off with merely a caution, a huge setback when you are trying to rebuild your life.
"Getting justice is essential to recovery after rape - cautions confirm that the authorities hardly count what happened to you as serious.
"Although there are some circumstances where a caution is appropriate, for example, where the perpetrator is very young, little comparable concern has been shown to teenagers convicted of non-violent crimes, for example those criminalised for graffiti and truancy via the use of Asbos."
Jim Gamble, head of the Child Exploitation and Online Protection Centre, who generated controversy earlier this month when he suggested not all paedophiles should be jailed, said it was important child sex offenders were dealt with properly.
He said: "Everybody doesn't go to prison, but let's make sure the right people do because that's the best way to protect our children.
"[A caution] is admitting you're guilty. It's being put on the sex offenders register and thereafter being monitored."