Given the conversations and debates that are going on in the media and in politics at the moment, it's never been more important that your children learn about consent at an early age. Their bodies are their own, and they shouldn't allow anyone else near them if it makes them uncomfortable. The same is true whether your child is a boy or a girl.
You have to remember that this also applies to you, too. You may desperately want to bundle your child up into a cuddle and smother them with kisses, but if they clearly don't want to, you shouldn't push the issue. They have to learn that it's OK to say no, and that if they say no, whoever wants to touch them should stop. It will teach them to enforce their own right to stay free of harassment in later life.