Get a good textbook and work through it. That should allow you to identify hiragana/katakana in the text. No need for children's books. To learn hiragana/katakana itself, just make flash cards or use a flash-card-like app. Also practice writing them.
You don't need to make a plan. Textbook authors have already done that for you. Follow the lessons, do the exercises. Ask us questions if needed. And wa-la you will know Japanese.