- Zachary Gordon (lots of TV) reprises his 2010 role as Greg, the Wimpy Kid, tormented by an older brother and goaded by his own ego into excruciatingly embarrassing moments, e.g., whitey tighties in a hotel lobby.
- Devon Bostick (lots of TV) is back again as Rodrick, that demonic older brother who torments his sibling, drums in a rock band, and tries to obey his parents.
- Robert Capron ("Diary of a Wimpy Kid") again brings heart to the plot. He is almost compelled to be honest.
- Karan Brar (uncredited) proves that even our Wimpy Kid isn't above turning around and tormenting someone else who is even wimpier.
- Rachael Harris (lots of TV) is our hero's exasperated mother, ineptly trying to negotiate a truce between her two oldest sons.
- Steve Zahn (lots of TV) is Dad, who has his own version of wimpy- dom, e.g., miniature civil war soldiers: "These are not toys! They are figurines!"
Of course this is written and filmed for adolescents, so everything is over the top, but the audience didn't mind; there was MUCH excited talk as the screening audience exited the theater...always a good sign. Dozens of those children came carrying their personal copy of a "Wimpy" book. That too, is a VERY good sign!