Children as young as one have fallen prey to paedophiles using the internet, with crimes including more than 100 rapes involving predators operating online in the last year.
The NSPCC said 38 police forces in England and Wales had recorded 3,186 sex crimes against children in 2015/16 that involved offenders using the internet.
Offences included sexual assaults, grooming victims, and inciting children to take part in sex acts. Most victims where an age was provided by police were 13 (535), but 272 were under 10 and the youngest was one.
This is the first year that police have been required to "cyber flag" sex abuse cases where the internet was used, although the NSPCC added that "a small number" of forces said they did not know about or were not using the Home Office scheme.
Chief executive of the NSPCC Peter Wanless said: "These figures confirm our fears that the online world is playing a significant role in the sexual abuse of children in the UK.
"It's clear that a large volume of sexual assaults and rapes of children have involved the use of the internet - for example by grooming victims before abusing them offline, or live-streaming the abuse.
"We know grooming is on the rise because children are increasingly telling our ChildLine service how they are being targeted online.
"Predatory adults posing as children try to meet them or blackmail them into meeting up or performing sexual acts on webcams, which obviously terrifies them and can leave some feeling suicidal.
"By revealing this first year of data we hope to highlight how police are under increasing pressure to cope with online offences so we have to ensure they have the resources and training to make them fit for tackling crime in the 21st century. And the Government must make mental health support available to every child who has endured abuse."
The figures were obtained via a Freedom of Information request to police in England, Wales and Northern Ireland by the NSPCC.
Anne Longfield, Children's Commissioner for England, said: "Sadly these concerning figures may be just the tip of the iceberg, because children rarely tell someone that they are being abused - often through fear of the consequences or because they cannot put their experiences into words.
"Successful police operations show that online sexual offenders use sophisticated methods to target, trick and groom children, and may target hundreds of children at a time. The internet is increasingly integral to children's lives and they need to be educated about the risks, as well as how to report suspicious behaviour.
"The effect of abuse, whether it happens offline or online is devastating, and we need to ensure therapy to help them recover from their ordeal is available."
Chief Constable Stephen Kavanagh, national lead for digital investigation and intelligence, said children are "desensitised" to meeting strangers in person who they have only previously had contact with online.
He cited research by West Yorkshire Police, which surveyed 2,500 secondary school children and found that 103 aged under 13 had arranged to meet someone in person that they had met online.
He said: "Grooming of children is hugely under reported and taking place on an industrial scale.
what we are seeing is children are desensitised to having contact with strangers who they only know through the digital age."