My sons (5 and 3) adored this book. It is a chapter book, but has some pictures in it. Sadly, it is a bit outdated and my sons kept asking me things like, "What's a phone booth" and such, but they still loved it.
The plot is that there is a little boy named Maxwell who doesn't really feel confident in himself. He notices that the water is going to flood the town so he calls out for help and ends up hearing a bunch of inanimate objects answering his call. Can he save the town?
After a week of raining, Maxwell, and his dog, Linda, leave their house, and discover that the town is about to be flooded. Maxwell thinks since he's only a third grader and small who has trouble concentrating that he can't do anything. But he soon discovers that sometimes even the smallest person can be a very big help.