Investigating child sex abuse cost police £1 billion last year and is set to treble by 2020, the top officer in charge of child protection has said.
Simon Bailey, chief constable for Norfolk Constabulary, said an increase in the number of cases was driven by the opportunities provided by the internet.
Children grow up watching pornography thinking that it is normal, thanks to the ease with which they can access it, he told The Times.
He said: "There has been an 80% increase in cases in the last three years, with police carrying out 70,000 child sexual abuse investigations last year.
"The average cost of each investigation is £19,000, so the police force is now spending a billion pounds a year on cases.
"If it continues at this rate we will be investigating 200,000 cases at a cost of £3 billion by 2020."
He initially believed that an increase in cases was down to more victims coming forward after DJ Jimmy Savile was exposed, but now believes more victims are being abused, both by adults who groom children and peer-on-peer abuse.
More than 20% of prosecutions involve under-18s, including incidents relating to gang abuse and those which start in consensual relationships but which escalate after young couples make a sex tape and one party threatens to release it, Mr Bailey said.
He described the impact of porn on young people, citing an instance where a 12-year-old put his penis into the mouth of a four-year-old girl and said: "Well, that's what you do Mum, I've seen it."
He called on internet companies to restrict access to porn to adults in the same way gamblers must prove their age before making bets online.
More undercover officers are being used to target those who groom young people online but Mr Bailey also wants better sex education provided by trained professionals as opposed to teachers, many of whom find it it too embarrassing.