I'm sure there's some diamat way to describe it. Adults are defined by not being children, children are defined by not being adults, but because they define each other they're in a dialectical relationship. There is a process where one transforms into the other over a process where quantity of time becomes quality of age, and after an even longer quantity of time it transforms again into a child-like end of life where we need to be cared for once again.

or something idk