My two-year-old niece Klubnikis is a very fortunate little girl. Since the day she was born, everybody respected her boundaries. Nobody tried to hug or kiss her if she didn’t feel like it. When Klubnikis’s Mommy and Grandma want to take a bath with her, they put on swimsuits. Nobody exhorts her to eat and nobody ever tells her “You will not leave the table until you finish this” when she doesn’t feel like eating.
When Klubnikis grows up, she will know that the only normal situation is one where nobody breaches her boundaries without her express consent, nobody unilaterally decides to get naked around her or to initiate tactile contact with her. This is not a lesson that it makes sense to teach in adolescence. You can exhort teenagers to “just say no” until you are hoarse, but if since early childhood they have been getting the message that nobody cares about their consent or lack thereof, it will be way too late to start delivering that message.