I think maybe he's Wonrei and Li-en's kid..? His eyes kind of look like Wonrei's, and it just makes sense that they'd have had a kid that Kiyomaro knows and has met, but hasn't seen often enough to recognize for sure.

It's kinda weird he doesn't appear to be wearing Chinese clothing though.

I saw another person suggest it's Dufaux's son we're just meeting. He certainly has the same attitude as Dufaux, and the design is similar...ish, but it seems a bit weird he wouldn't have the same eyes as his father in that case. It's such a big part of Dufaux's design.

I don't think I buy that though. Elly was kinda reserved, but not so much that I think she wouldn't be happy to see Kiyomaro/Gash. Plus, why would she not just be called Elly? And why would she not ask about Earth?

I'm pretty sure this is a new character. Question is, why does Kioymaro know them?

Catching up on Zatch Bell 2 (spoilers ahead):

Who is Fern?

This series is a decent while after original Zatch Bell. This kid is.. maybeee young enough to have been born at the end of the series? I saw some people online suggest it's Elly, because apparently Elly had boyish dialogue in Japanese(?)