The animal-themed pet names are a Iuilic thing. So Tansy and Thorn will call Hyacinth “chickadee”, while Larch defaults to “kiddo.”
Larch: It isn’t just you they tried to contact behind our backs today, kiddo. Your grandma was cold-calling childcare centers, trying to pick up Hawthorn without us knowing. They were here until just a bit ago! Your uncle Thorn scared them off.
Tansy: There’s no reason they can’t try again. We should set up some kind of family password —
Hyacinth: Uh, we already have that.
Thorn/Hyacinth: “Franklin Roosevelt.”
Hyacinth: From when I got into that Safety Ideas For Children book — remember? It was years ago.
Tansy: Oh! That sounds familiar now. I think we used the wacky alien name because I didn’t take it seriously.
Hyacinth: Well, Hawthorn did.
Thorn: And we’re all lucky that Hyacinth remembered.