However a slight variation about joking with kids that I find does work surprisingly well is the totally exhagerrated consequences. But it really has to be totally over the top and utterly unbelievable, the sillier the better. It simultaneously breaks the impending mood of conflict, makes them laugh, while somehow actually motivating them to do what they are resisting. We all know it won't be the real consequence of them (not) doing whatever, but it still seems to work. It's weird. Doesn't always work of course (nothing with kids ever does), but a variation on the theme has frequently helped.
I've often done that with my own kids, once tried it with a child at my work - trying to none with them - kid took it seriously and screamed the place down. No young kids get sarcasm, but lots don't get exposed to silliness and so will believe even ludicrous stuff from parents. That child taught me well!
I think people often underestimate the role trust plays in humor (with both kids and adults). This explains why some pretty awful jokes can be funny when coming from someone you know intimately but not from a stranger, and why your kids find it funny when you suggest xyz as a consequence, but someone else's is horrified.
However a slight variation about joking with kids that I find does work surprisingly well is the totally exhagerrated consequences. But it really has to be totally over the top and utterly unbelievable, the sillier the better. It simultaneously breaks the impending mood of conflict, makes them laugh, while somehow actually motivating them to do what they are resisting. We all know it won't be the real consequence of them (not) doing whatever, but it still seems to work. It's weird. Doesn't always work of course (nothing with kids ever does), but a variation on the theme has frequently helped.