My kids don't like grammar to begin with, you might be thinking. How am I supposed to get them to do even more of it?
While it's true that grammar isn't usually a favorite subject, it's also true that it's one of the most foundational. Until the nineteenth century, most education was focused primarily on grammar and the language arts, and even today this method is enjoying something of a revival with the interest in Classical education. Understanding language is so essential because it's the way all other knowledge is transmitted and received.
Grammar in particular reveals the way language works. The rules of English regulate its use so that communication becomes intelligible, so that we can understand each other. Kids need to know this so they can A) understand what they read and hear, and B) make themselves understandable to others.
Few of them will want to do this initially, but the more they understand the easier it'll become. Grammar resources can help them reach the "second-nature" stage, and make a normally boring and difficult study fun and interesting. There's no law that says grammar needs to be boring, or that creative methods of teaching it should be avoided.
Ruth Heller's World of Language books are a great place to start with younger students; each slim volume is beautifully and brightly illustrated, and introduces parts of speech and their usage. Grammar Songs gives kids catchy ditties to help them remember the essentials of noun-verb agreement, irregular verbs, punctuation, etc. (These songs can get pretty annoying real fast, but they do the job!)
For older students, E.B. White and William Strunk's The Elements of Style offers a laugh-out-loud funny guide to how to use (and how not to use) language in writing. A classic immediately on its publication, this is still among the standard texts for college students and creative writers. On the more straightforward side, 501 English Verbs is exactly what it sounds like, offering conjugations of the most common verbs in English. And these are just a couple options: good grammar resources are widely available.
None of the books offered here are comprehensive enough to be used in place of a grammar curriculum. They are, however, an excellent way to supplement and generate interest in an often overlooked or hated subject. In addition, we encourage parents not to express distaste for grammar study; kids often simply reflect the attitude they learn from mom and dad, so if you're enthusiastic, they likely will be as well.