I've been teaching myself Japanese for nearly two years now. I started because I thought it would be fun to learn with my two daughters--not realizing how unrealistic it was to think I could teach a language I didn't speak myself. I became intrigued with the challenge of teaching myself and while it is difficult to find time to study and sometimes I feel so far behind other students I meet who've been studying for two years, it's really gratifying to be able to read something, even if it is a children's book.
I used the book Japanese For Busy People I as my first textbook. I really liked it, and started on the second book--I am having a lot more trouble with. It seems as though they use a lot of kanji they don't explain. I also use Japanese the Manga Way. Initially I was put off by the manga aspect, but it does a great job of explaining grammar. And since it's been a long time since I studied English grammar, it helps a lot! For kanji study I use Guide to Reading and Writing Japanese. It's not the best resource as it uses romaji instead of kana, but it's really cheap.
For online sites, this is a fun one to start out with:
Kids Web Japan
Good grammar resource
Tae Kim's Guide to Japanese Grammar
Jim Breen's WWWJDIC
Another fun vocabulary page. If you scroll to the bottom and click on Home, there are other language options
One of the best study aids was finding out that a local library subscibes to Rosetta Stone, all I needed to do was apply for a library card and I can now access it for free--including all the languages. A wonderful bonus, since just buying the software for one language can cost nearly 300.00 and I access all languages for free.
And of course Yesasia for Japanese language books.
Miranda isn't terribly interested in learning Japanese, although she does enjoy watching movies and cartoons. Reading the subtitles has been good practice for her reading skills as well. Ivy is more enthusiastic and has been practicing writing Japanese along with learning the English alphabet. She's getting pretty good.