Encourage (require) your children to edit their own writing. Teach them early that their first attempt is not their final product. This is where I do the bulk of grammar teaching. It's not my hacking the paper with a red pen and making the student feel like a complete grammatical loser. Rather, it's sitting with the child, who doesn't believe in periods or apostrophes, and having him find where he can insert a few. Or it's showing the importance of signaling dialogue with quotation marks or making another paragraph each time a new person speaks. This works well because the student is seeing the immediate connection between grammatical rules and his own work.