Deaged Harry, Ron, and Hermione (like in Trio but younger) are found by Mal, Zoe, and whatever crew they have at the time (none?). At first Mal plans to get rid of them ASAP, but he comes around, at least partly because of Harry's terror of being sent to an orphanage. As in Trio, Harry's not all there, so it's not exactly shocking that he and River get along like two peas in a pod once the Tams come aboard. All three of them act childish most of the time, because except for Ron they didn't when they were young the first time; Ron acts the most mature most of the time.

[River freaks out about Book's hair]
Harry: Don't worry, it only attacks his enemies.