Indexicals, Children, and Kant

I was corresponding with a distinguished philosopher about the shared affection of our small children for indexicals and possessive pronouns (such as "me" and "mine"). My anecdote about my oldest, when he was 2:

Father: "I'm me, you're you."

Son: "No, I'm me, and you're you."

Father: No, I"m me, you're you."

Son: "No, no, no, I'm me, and you're you."

etc.

Debates about "me" and "you," this philosopher noted, soon give way to reflections on "me" and what's "mine." This philosopher observed: "Kant got it all wrong about the basic categories of conscious experience. Concepts of possession beat those of causality and substance any day." Indeed!