A total of 449 sex offences were committed in the past year against babies before they reached their first birthday, figures obtained by the NSPCC have revealed.
UK police forces recorded 73,518 crimes, including rape, online grooming and sexual assault against children in 2019/20, similar to the 73,379 the previous year, but up by 57% from 46,738 in 2014/15.
More than 8,000 offences were committed against 14-year-olds, while 12,374 sex crimes were recorded against children under 10, and 449 against infants yet to turn one.
The data suggested girls were four times more likely to be victims than boys.
The figures come from 44 of the 45 police forces across Britain, but do not include Greater Manchester Police, which did not provide information.
NSPCC chief executive Peter Wanless said the "crisis of child sexual abuse is not going away", adding that "behind these figures are thousands of children and young people who have reported crimes that can have a devastating impact on their lives".
"Urgent action is needed to prevent abuse and to ensure children are supported to recover when they bravely speak out," he continued.
The new figures come as an NSPCC report found that the number of people contacting another charity, Childline, for help following sexual abuse in the family had tripled during the coronavirus pandemic, with an average of 23 per week since 23 March.
"It started during lockdown," one 17-year-old girl said.
"I don't want to live here anymore. I feel I should tell social services about how abusive dad is, but I don't feel ready to tell them about the sexual abuse part."
The NSPCC is calling for the government to publish its strategy to tackle child sexual abuse announced by then home secretary Sajid Javid in June last year, and for departments, including the Home Office, Department of Education and Ministry of Justice, to join up efforts to prevent abuse.
Safeguarding minister Victoria Atkins described the figures as "truly sickening", adding that "the government has made it a priority to lead the global effort to tackle this crime, safeguard victims and bring perpetrators to justice".
She continued: "We have hosted the Hidden Harms summit, collaborated with Five Eyes partners and convened a global conference to drive the response as well as invested in law enforcement and boosted funds to charities, including the NSPCC which received Â£1.6m towards its helpline.
"It is right that we prioritised children at an immediate risk during the pandemic and are now working towards publishing our first of its kind national strategy on tackling all forms of child sexual abuse by the end of this year."