I bought a few books on Bryce Canyon and Zion while planning our family vacation and this book was the most useful and helpful. We just returned from the trip and were very happy with this guidebook.
The book provides all the information needed to plan your trip to the parks, including when to go, what to take, and any permits needed. There is also information on where to stay and camp, and also where to eat - though we ended up bringing most of our food with us and cooking on a camp stove.
The book has great guides on best day hikes. This was particularly useful since we have two young boys - 4 and 6. We did a lot of day hikes. Our favorite hike was the Queens Garden Trail. We did that one twice - it is only about 2 miles round trip with great views!
Overall, this is an incredibly useful book that easily fits in your backpack!