Released right when summer starts to drag, Diary of a Wimpy Kid: Dog Days at least doesn't add to the exhaustion. It's the latest installment in what now forms a lightly likable trilogy of films based on Jeff Kinney's Wimpy Kid books, notebook-paper-doodle-illustrated young-adult epistolary novels that record middle schooler Greg Heffley's navigation of the multitudinous perils of a suburban childhood and its prefab identity options. If there's a secret to the popularity of Kinney's books, it's that they understand kids' healthy, conspiratorial disrespect for everything the adult world encourages them to take an interest in, while never settling into lazy Garfield cynicism. Summer break is the pertinent problem this time around. Against the wishes of his father, Greg conspires to spend every day inside playing video games but has to whip up an illusion of responsible activity as a smoke screen, including a fake country-club job and a stint with the Boy Scouts. Zachary Gordon practices his well-honed wince as Greg, leading a returning ensemble cast that includes Robert Capron as amiable butterball best friend Rowley Jefferson and Steve Zahn, used to good advantage here as the oft-hyperventilating patriarch Frank Heffley. The humor ranges from broad shame-based comedy (swim trunks lost on the high-dive board) to moments of subtler discomfort, like a seaside vacation with the Jeffersons that comes to a dead halt around a touchy-feely game called "I Love You Because."