My children have an awesome vocabulary, and it hasn't been a huge focus in our homeschool. My 15 yo just told me yesterday that throughout the years, if he is reading and doesn't know a word, he will often get out the dictionary to find out what it means, or he'll just figure it out from the passage. He also said that the the Redwall series by Brian Jacques helped him tremendously with his vocabulary. He first read the series in the 3rd grade, and has re-read the books numerous times throughout the years. My oldest son has always loved words. When he was 9 yo he wanted a dictionary for Christmas. It was one of his favorite gifts! The other favorite that year was an X-Box :).
One thing I have done is instill in my kids a love of reading. I've read to them just about everyday from the time they were babies. I love books, and I love sharing them with my children. My husband has an incredible vocabulary, and a love of words that he has passed on to our kids. I was inspired to write this post after reading Heather's post at Blog,She Wrote.