Of varying levels of completeness:
1. Publish a children's book series with more than sixty books over the course of five years and let it become popular.
2. Okay a mediocre television series inspired by/half-based on the books.
3. Finish book series (still aimed at middle schoolers) and move on to other things.
4. Wait ten years and re-release books with new covers and corrected errors.
5. Reach an even wider audience: the old readers and the new readers.
6. Use the new demographic along with the one you planted 15 years ago to securely launch a new TV and/or film series that more closely matches the books.
7. ???
8. PROFIT! (over a really long time)
That's kind of what they did with the Harry Potter series:
1. Publish the American edition of a British children's book series.
2. Within a few short years, okay a film to be made on the first one.
3. Allow the book and film series to grow in popularity as the fanbase grows larger and older.
4. Finish the series with a darker, mature, young adult book and a dark film.
5. Possibly merchandise.
6. ???
7. PROFIT! (even more $ and faster)