Me, I stick with Stephen Krashen's hypothesis, borne out by my own experience: compelling, comprehensible input is the key. This applies to both your first language acquired when you are young and any other languages later.

Start with reading to kids, then give them access to wide selection of books to choose from. Comic books are good, too.

I have many criticisms of the education I received as a youngster, but they did get this right.