Reddit mentions of When I Feel Worried (The Way I Feel Books)

Do you mean books for him or books for you to read about helping him?

For you, I've heard good things about Freeing Your Child From Anxiety and The Opposite of Worry. There's also a lot of great information on this website.

For him, it really depends on what the anxiety is about - does he have specific fears, or get anxious around separations from you, or at bedtime? I can probably give you more specific suggestions with more info, but some good general ones are Worries Are Not Forever, When I Feel Worried, The I'm Not Scared Book, and My Magic Breath. There are also some great books about emotions more generally such as My Many Colored Days, Visiting Feelings, and How is Daniel Feeing? which will help improve his emotional vocabulary and teach broader coping skills.