I’m not saying your child is rebellious, but this post explains how you can reach your child’s heart: https://www.imperfecthomemaker.com/2015/04/10-ways-to-reach-the-heart-of-the-rebel.html

I would say it’s extremely important to read it now while your kids are little! You’ll have a huge head start since you can teach them these things from the get-go instead of trying to go back and undo bad habits! But to answer your question directly, the specific examples of training activities given in the book cover a wide range of ages — including the very youngest children.