I'm a big believer in the importance of consent and stressing it when kids are young. My (many!) goddaughter and/or nieces and nephews all are told by me they have the right to consent to what happens to their body. They can opt out of being tickled, they need to ask me consent before jumping on me they way they can hurt me etc etc.
Of course now that my goddaughters have gotten the idea of consent their trying to take it to the logical extreme by telling their mothers that they don't consent to anything they don't like. The problem is their still kids and some things still have to happen. They still need their baths, they still might get physically put into time out, they still need to get checkups etc. Most relevant to this question is that they both have that interacial curly hair that can be a pain to maintain and want it long but don't like the time, and occasional pain of dealing with knots, that comes with trying to keep it properly maintained. So of course they respond by saying they don't consent to having these things done to them, after all we keep telling them they need to consent to anything done to their body so why shouldn't they get to use that power here?
So what is the best way to explain why they are going to have to get their hair done, or whatever physical activity they don't like, even if they don't consent? How do you explain that consent is super important, but at their young age they still don't yet have 100% control over that right to consent yet?
Note: Just letting their hair become a tangled mess (and/or cutting it) or otherwise never doing the thing they don't want isn't really an option. I'm not the parent and I don't really get to decide how the parent's deal with such issues. I'm more interested on how to explain why they don't get to opt-out of some things despite the stressing of consent.