White Ribbon, a charity aiming to engage men and boys and end violence against women and girls, said the hundreds of cases nationally are still too high and urged the Government to increase funding in education.
The Home Office said it is "determined to tackle sexual abuse" and is rolling out guidance on how to teach children about sexual harassment, sexual violence and violence against women and girls to prevent children from committing further sexual offences.
The latest figures from the Youth Justice Board for England and Wales show five sexual offences led to Devon and Cornwall Police sentencing or cautioning an under-18 in the year to March – down from 17, and the lowest number since records began in 2013-14.
Across England and Wales, the number of offences leading to children sentenced or cautioned for committing a sexual offence fell by 2% to the second-lowest figure since records began in 2011-12, from 903 to 884.
Only in 2019-20 did police record fewer proven offences (881), while the total number has more than halved since 2011-12.
Anthea Sully, chief executive of White Ribbon, said: "Despite this being a reduction in numbers, it is still far too high, and behind every number there is still a story of very real harm.
"There is not nearly enough funding put into preventing this work in education settings.
"Unless the Government commits to this, there will continue to be children where lifelong harm is caused."
A Government spokesperson said: "We are determined to tackle all sexual abuse, including violence against women and girls, and to keep children safe."Relationships, sex and health education has been made a mandatory part of the school curriculum, helping pupils learn about these subjects in an age-appropriate way."Later this year we will also issue further non-statutory guidance on how to teach children about sexual harassment, sexual violence and violence against women and girls in order to help prevent these crimes from taking place in the long term."
A total of two serious offences, such as murder, violent crime or some sexual offences, led to a child being cautioned or sentenced in Devon and Cornwall last year – of these, two were sexual offences.
Meanwhile, Devon and Cornwall Police arrested 906 children for all offences in 2021-22, equating to 5.9 per 1,000 children.
Arrests for sexual offences rose by 64% across the country, from 1,700 to 2,900.