This "What to Do" series was very useful to me as a parent. It explains complex psychological ideas at a child's level without condescending to them and then attempts to help them learn how deal with those strong emotions.
I purchased this book and What to Do When You Worry Too Much: A Kid's Guide to Overcoming Anxiety (What to Do Guides for Kids) after my 5-year old was diagnosed with Type 1 diabetes. It has helped her and her then 8-year old brother work through the many adjustments in our family after the diagnosis. We went through the book together and then talked about the activities that might help them deal with how they felt. The simple, clear explanations were a great starting point for discussion. Not everything "worked" nor did we focus on "solving" these emotions--rather we used the books to help the kids see that they are not alone and that there are things they can do when they feel trapped by strong emotions.
My daughter is now almost 7 and still takes the Grumbling book out to read it over. She knows she does have things to complain about in her life, but also that she doesn't want them to take over her life. I have also just purchased What to Do When Your Temper Flares: A Kid's Guide to Overcoming Problems With Anger (What to Do Guides for Kids)which she is anxious to read! How many books on these tough topics can you say THAT about?
If you have intense, thoughtful, strong-willed kids, this approach to the perpetual problems of grumbling, worrying and (I hope) anger management will help. And even if they won't read it, it will help you know how to talk about those feelings.
P.S. Another good book is Who Moved My Cheese? For Kids I know it sounds corny but change is a big stressor for my kids so that book helped address these emotions too.