In the "How to Use This Book" section of First Language Lessons for the Well-Trained Mind, Jessie Wise states, "I believe we underestimate what young children are capable of learning." Wise's method is to cover grammar rules, definitions, and correct usage through memory work, copying and dictation, narration, and repetition. Each lesson is short, about 5-10 minutes per day on average and scripted, making preparation time for the teacher minimal. There are 100 lessons for first grade and 100 for second grade although I believe a child in 3rd or 4th grade with no grammar knowledge would enjoy these lessons as well, making this book perfect for using in a family with children of multiple ages. The child answers questions or repeats definitions orally.
In the book, she covers the definitions of nouns, pronouns, adjectives, adverbs, conjunctions, prepositions, articles, verbs, etc. She also covers types of sentences, seasons, days of the week, months of the year, story narration, abbreviations, letter writing, synonyms, antonyms, poem memorization, and much more.
I used this book with both of my boys, and they both learned so much. My only criticism of the book is it's emphasis on copywork and dictation. For boys, especially, memorization and answering orally comes much easier than writing. When writing is difficult in a motor-skills-type-of-way, as for many boys and some girls, then copywork and dictation can become boring, painful, and tedious. So, we just skipped all that. Also, towards the end, we did not memorize some of the longer poems.
About 3 days a week, we sat down and read through the lesson, following the script pretty much as it was written. My youngest was sad when we finished this book. You can't get a better endorsement than that.
If you are looking for something that teaches your young children grammar with little teacher prep, then try First Language Lessons for the Well-Trained Mind.