Police forces in the UK recorded 64,667 sexual offences against victims aged under 18 in 2016/17, according to figures obtained by the NSPCC.
It was a rise of 15 per cent compared with the previous year, and equates to an average of 177 a day.
The NSPCC said recorded offences included rape, sexual assault and grooming.
In nearly 14,000 cases the alleged victim was aged 10 or under, with 2,788 offences allegedly committed against children aged four or under.
Researchers found that one in 10 offences recorded was flagged as having an online element - up by more than half year-on-year.
The increase in recorded child sexual offences was described as 'dramatic' and 'extremely concerning' by the NSPCC.
It said possible reasons for the trend include improved recording methods, survivors feeling more confident in coming forward and the emergence of online groomers as a 'significant problem'.
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.
"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."
The charity compiled the data after submitting Freedom of Information requests to forces in England, Wales, Scotland and Northern Ireland.