There’s an important difference between allowing a child to be free and not caring what they do. If you allow another person freedom, or rather if you refrain from trying to limit their freedom, it’s possible to have an honest and open relationship, in which case you can express your worry about stuff like excessive consumption of junk food and TV. Children are usually pretty attentive and open to this stuff when it comes from someone they can trust, which has to be someone who isn’t busy oppressing them. Besides, children who are free and in a supporting, healthy environment don’t generally end up vegetating in front of a TV – that’s not the behavior of a free person, but of a person trying to run away from something.
One has to be careful not to judge free children based on experience with children raised in oppression. Peter Gray has written often about how psychology makes this mistake, with “developmental psychology” actually being “psychology of children in traditional schools”, as though the traditional Industrial school is the neutral, natural environment for children to be in.