But you can't agree to consensual sex under the age of 16, so legally it is child abuse
For clarity regarding The Age of Consent (Sexual Offences Act 2003)
The legal age for young people to consent to have sex is still 16, whether they are straight, gay or bisexual. The aim of the law is to protect the rights and interests of young people, and make it easier to prosecute people who pressure or force others into having sex they don't want.
For the purposes of the under 13 offences, whether the child consented is irrelevant. A child under 13 does not, under any circumstances, have the legal capacity to consent to any form of sexual activity.
Although the age of consent remains at 16, the law is not intended to prosecute mutually agreed teenage sexual activity between two young people of a similar age, unless it involves abuse or exploitation. Young people, including those under 13, will continue to have the right to confidential advice on contraception, condoms, pregnancy and abortion.