Grace may be a certified baby but he is still a scientist and his specialist interests are still Space and Alien and golly gee willikers you'll never guess where he is and with whom. So like I feel like a lot of his interactions with Rocky while regressing on the ship would be like this.
Rocky: Eridians do not cry. Eridians do not have eyes. Grace knows this, statement.
Grace, frustrated: But- I know. But when you're sad- cuz when I'm sad, I cry- ?
Rocky: Baby Grace want to learn what Eridians do when sad, question?
Grace: *nodding* yes. ...please.
Rocky: Grace sit down. I will teach about Eridian feelings.
Rocky: What Baby Grace doing, question?
Grace, struggling to put on his space suit: I'm gonna go on a spacewalk!
Rocky: No. Grace stay on ship.
Grace, pausing and immediately tearing up: What? Why?
Rocky: Grace is baby today. Space not safe for babies. Baby Grace stay on ship.
Grace, beginning to sniffle: But-
Rocky: Non-negotiable. Safety is most important. Grace can do spacewalk when baby time is done.
Rocky: Good listener Grace. Look out window instead?
Grace, perking up: Maybe I'll see a nebula!!
Grace: What's "spaceship" in Eridian?
Grace: Oooo. What's "friend"?
Grace: Rocky, you're my *bad whistling*
Rocky: ...Good try. Baby Grace also my ♬♩♬♫♪.