[Her reaction feeds his joy, but it almost makes him laugh at the same time. Since her reaction is only a shadow of how the older her would react to the news firsthand.]

Thanks, Katara. It's my youngest boy who's an Airbender. And I have two older troublemakers who I love just as much. [Pause.] I'd love to tell you details, Katara, but... I'm not sure what would be wise. You're still so young, after all, and some things might sound weird coming from Old Man Aang. [He smiles and absentmindedly spins some pebbles around his raised pointer finger with Airbending.] But hey, if there's anything you think you're ready to know, I'll tell you.