Well, yes, of course I'm serious. I agree that children aren't experienced enough themselves to have that ability - hence the word 'teach'. The worst thing you could do with a child, I think, is to suggest that absolute unquestioning, uncritical obedience to rules - any rules - is a good thing. Obviously, you help them work it out - you help them learn which rules, even if they are arbitrary, frustrating, etc. should be kept for their own (or the greater) good, and which they should probably accept only under duress.
If you teach them well, then they should be able to understand why they need to get up for school, and why they can't drive at age 10. But you can also help them see that 17 as a legal driving age is itself arbitrary - nothing magically changes at midnight the day you turn 17. It's a rule with a good reason behind it, but that shouldn't stop them thinking about it critically.
Do I think 14 days self-isolation with no exercise is appropriate, ethical or moral for children who are not sick or at all likely to be infected? No, I don't.
I'm not unable to see your point of view. I can see that if you genuinely feel that people taking their kids out for a brief walk every day is making lockdown longer, or risks killing people, then you must be both outraged and frightened. But many of us - including on this thread - do not think that either of those things are true. We are not being selfish (or no more than anyone else) - and it's not that these points haven't occurred to us. But we do not think the rule is entirely right and we do not think that our actions will cause harm.