He was two. I used color stickers on a keyboard, using the We Hear and Play system: http://www.wehearandplay.com/

The Japanese method is based on chord identification, but I found that note identification worked directly. Play a note, point out a toy of that color. Kid brings a toy, play the note for the color. Kid plays a note, you bring a toy. Color association is the tool that lets you connect the music to everyday things and make up all kinds of natural games that interact with the kid’s interests.