The NSPCC says an average of 177 alleged sex crimes against children a day were recorded in 2016/17, a record high.
In all there were 64,667 reported offences against children under the age of 18, an increase of 15% on the previous year.
Offences included rape, sexual assault and grooming.
In almost 14,000 cases the alleged victim was aged 10 or under, with 2,788 allegedly perpetrated against children aged four or under.
In 10% of cases there was an online element involved.
The figures were compiled from Freedom of Information requests submitted to forces across the UK.
NSPCC chief executive Peter Wanless said: "This dramatic rise is extremely concerning and shows just how extensive child sexual abuse is.
"These abhorrent crimes can shatter a child's life, leaving them to feel humiliated, depressed or even suicidal.
"That is why it is crucial every single child who has endured abuse and needs support must get timely, thorough help so they can learn to rebuild their lives."
The charity says improved recording methods, survivors feeling more confident in coming forward and the emergence of online groomers as a "significant problem" could all have contributed to the increase.
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Mr Wanless said: "These new figures suggest the police are making real progress in how they investigate sex offences against children.
"To help them tackle the issue going forward, we must ensure the police are equipped to work with other agencies and provide ongoing support and training to officers on the front line."