Starting young is the best time!
Shannon's English School encourages that students as young as 3 years old start classes in order to enjoy English from a young age. It is important to get children to listen in English and to pronounciate many new words and sounds that makes English different to Japanese. We use a lot of songs at this age is it helps to reinforce the sounds of the words and makes learning more fun.
Here is a great example of kids using English songs to remember and use words for the future:
