You're still ahead of me, at the moment, watched episodes 3 and 4, but thought I'd wait until the subs are out to watch episode 5!
Technically all chosen children didn't feature at the start of Adventure, or at least get whisked away to the Digital World, as Hikari was home, sick! I'd say that each series is different, as I think Savers didn't introduce us to everyone at the start either, I think we only got introduced to Masaru and Yoshino in the first episode!
Been enjoying Appmon, I find it a quite zany series, although I do agree with a comment on the site that I was using to wat