Parents need to know that The War with Grandpa is a family comedy based on Robert Kimmel Smith's 1984 book about a resentful boy named Peter (Oakes Fegley) who pranks his grandfather (Robert De Niro) in hopes that he'll move out of his room. Eventually, Grandpa engages, and the two start a "war" that actually ends up creating a bond between them. If you can suspend your disbelief, it's funny enough, and it promotes the value that a relationship with grandparents can add to kids' lives. But Peter's tactics come off more mean-spirited on-screen than they did on the page. His "pranks" cause many accidents for Grandpa and his elderly friends, including electrocution and falls that in real life would cause broken bones, cracked skulls, or even death. A recurring joke involves Peter's older sister being caught kissing her boyfriend (though the actual kissing is never shown), and the older characters have a couple of jokes about drinking (and they spike their own drinks). Mild language includes "hell," "boobie," and "wiseass"; there's also some potty humor, a glimpse of a character's underwear, threats, and remarks about a bully punching a kid in the face.