Okay, so we've got Aredhel chronically wandering off as a running gag - works for me.
Attempt at a conversation, take 2:
*Galadriel enters a room containing Aredhel and a blond-haired toddler. Aredhel and the toddler are laughing together about something.*
Galadriel: What are you two up to? Secret plans?
Idril: Plans! *giggles*
Aredhel: Oh, Galadriel, good to see you! Idril and I were just talking about going to visit her uncle Fingon later, weren't we?
Idril: *announces proudly* I'm going to marry him!
Galadriel: *shakes her head* You can't marry your uncle, silly.
Idril: Why not?
Aredhel: *bends down to her level* Because you're related. We don't marry people we're related to. That's not how it works.
Idril: So I can't marry anyone I know?
Galadriel: *to Idril* You have some time to think about it, don't worry. *to Aredhel* So you are headed to Fingon's house soon? My brothers are there now.
Aredhel: Oh, do you want to take Idril then? I told her parents I would bring her, but last time... *laughs* we arrived so late everyone worried about her.
Idril: *puzzling things out* *to Galadriel* So, are we related?
Galadriel: Yes! Your dad and I are cousins.
Idril: What's a cousin?
Aredhel: When brothers and sisters have children, those children are cousins. You don't have any cousins yet....
Idril: Because I don't have any brothers or sisters?
Aredhel: And because Fingon and I aren't married and don't have any children.
Idril: *thinks about it* Who are your cousins?
Galadriel: I have a lot of cousins! Your aunt Aredhel and uncle Fingon, and your dad are all my cousins. But I also have cousins in Alqualondë, because my mother is from there, and her brothers have children.
Idril: Will I get to visit Alqualondë some day?
Galadriel: Of course....
Aredhel: *interrupting* And we have cousins in Formenos.
Galadriel: Half-cousins.
Aredhel: They're still cousins.
Galadriel: They never let us forget that it's half-cousins.
Idril: *confused*
So that is way too rambling, and barely even serves as a transition between other scenes, and never manages to name Turgon as Idril's father...but, there you go! I like tiny!Idril better than tiny!Galadriel, I think.