If sexual autonomy was conferred upon children, imagine the field day all perverts would have, for now they could claim, "I did nothing wrong, only what the kid wanted me to do, per his/her right of sexual autonomy.".
Children shouldn’t be sex slaves. Libya is on that list and Libya is well known for sex slavery as well as quite a few other unsavory practices.
“Autonomy” can mean both not enslaving people, but it can also mean the mess we are seeing with allowing minors to make choices that will undermine their health for the rest of their lives.
I’m personally in favor of minors not being exploited.