Children can learn more than one language at a time. Perhaps the best way to expose your children to the Japanese language is to speak it to them yourself, according to PBS.org. If that's not a possibe, or you want to offer additional learning experiences for your child, you have several choices to fit with his learning style.
A software program can offer a well-rounded approach to learning Japanese, because your child will be able to hear native Japanese speakers speaking in Japanese, along with learning the written language. Kids Japanese 2 is an app that teaches some basic vocabulary words, along with starting to learn the Japanese alphabet. An older child might enjoy Rosetta Stone, which teaches conversational phrases and records her voice so she can hear how well she's doing.
With brightly colored pictures and fun characters, videos can entice your child to learn Japanese. Get started with made-to-teach-Japanese videos such as those offered by Little Pim or Dino Lingo. Dino Lingo even has accompanying workbooks and flash cards. Once your child has the basics down, he might enjoy watching real Japanese programming for kids, such as Anpanman or Shimajiro, which are readily available on YouTube. Older children might like Naruto, which you can stream on Netflix, or Sailor Moon.
Genko yoshi is the Japanese equivalent of writing paper with dotted lines. It features small boxes that students use to practice their handwriting. Start with hiragana and katakana, which are the phonetic "letters" that make up Japanese, then progress to kanji, the more pictorial characters. When your child understands how to read Japanese, it can improve her pronunciation, since Japanese is a phonetic language.
A book such as "Ah So! Japanese for Kids" can work well to teach younger elementary-school children Japanese. Older students might like a more traditional Japanese text book, such as "Japanese for Busy People" or "Minna No Nihongo." Aside from those books, it can be helpful to read other books in Japanese, if you can read hiragana and katakana. Through Amazon.co.jp, you can order the Japanese versions of classic tales such as "Goodnight Moon" and "The Very Hungry Caterpillar." Because your child is already familiar with the story, he can understand what you're reading, even if he can't understand every word.