When our son was still a baby, we decided, for various reasons, to start teaching him Japanese.
This was more difficult because we don't speak Japanese, although I learned a little in high school and can still read Hiragana.
This is what we have done so far:
He and I took a parent-child music class that was in Japanese. It was very cute!
We got some CDs of children's music from the library and played them in the car.
When he reached 3.5 the school that supported the music classes offered us a spot in the junior kindergarten class (everyone was expected to register, it was basically the next level up) so he has been taking a class every Saturday during the school year for a year and a half now.
Last summer we signed him up for a Japanese daycamp. He enjoyed this and asked to sign up again, so he ended up doing this for 3 weeks.
We then signed him up for an afterschool class at the place that runs the daycamp, so he now has two classes per week.
I try to read to him in Japanese as much as possible, but when I'm tired or we get busy I lose focus. I'm hoping that if I make a blog about his progress, I'll be more motivated to do the small daily activities. He also wants to learn French because some of his friends are in French Immersion. We plan to start French once he's more comfortable with his Japanese. Since we can't do simultaneous bilingualism, we are doing sequential bilingualism, and I think adding the French now would be confusing.
Right now, he can sing a few songs, write his name, knows about a thousand words, and can say please and thank you appropriately. We are working on asking questions. I'm not sure what they're working on in his classes other than hiragana. Most of what I see on parent days are the cultural events, which I think are very important. I think one of the main advantages to learning a language is gaining knowledge of a culture and if he can do this with other children? It's definitely worth it.