The Johnny and Jesse's storyline and numerous parallel interviews have one particular goal — to show how important it is to listen to the younger generation. It is unacceptable to turn a blind eye to the problems that seem inappropriate for a child's age, to smile condescendingly instead, and the director is trying his best to show it. Children's reflections and experiences do not deserve indifference, and it is this immutable truth which is the overarching theme of the entire plot and every dialogue.
Johnny and Jesse are not just "uncle and nephew", they are friends, colleagues, associates. Each of their conversations has a therapeutic effect, and for both of them. Johnny teaches Jesse that "You can be "not fine" and that's okay", and Jesse poses questions that force Johnny to think about the nature of his painful feeling of emptiness. He makes him think about why he doesn't talk to his sister much and why he got so angry when Jesse got lost for just a few moments in a tiny store. For Mike Mills, it's as if there is no "child" and "adult", there are just "people". Age boundaries are erased, only human feelings remain, which do not have age limits and life experience boundaries.