Math for Smarty Pants by Marilyn Burns (Little, Brown, and Company, 1982) is a book for kids that illustrates the fun side of math. The book is similar to, but written for a slightly more advanced audience than, The I Hate Mathematics Book, another book by Burns from the same series (Brown Paper School), so Math for Smarty Pants could be considered a sequel to that book.
Math for Smarty Pants starts by defining many ways in which someone might be "smart in math;" it isn't just about being good at arithmetic. There are seven chapters ("Arithmetic with a Twist", "The Shapes of Math", "Math for Two", "Logical Puzzles", "Statistical Stuff", "Math Trickery", and "Thinking Big"), each of which contain many examples of mathematics made fun, such as amusements, puzzles, games, riddles, and other recreations. To take one example, in chapter 2, "The Shapes of Math", which is 14 pages in length, the table of contents lists 18 activities, such as "Don't Make a Triangle," "Geometry Joke," "Quick Change," "Pictures of Math," and so on. There are five main characters in the book (all children) that appear throughout the book discussing various topics with one another, which may make it easier for the reader to relate to the material.
Even though the topics are geared for children, the topics aren't trivial and meaningless—many of them provide ample room for further exploration. Some even touch on unsolved problems. For example, the "Mathematical Stunt Flying" section mentions the (still not yet proven) Collatz conjecture, although not by that name, and the section on perfect numbers briefly discusses the (unsolved) question of whether there are any odd perfect numbers. Even in other sections, questions are raised that could give the curious reader a lot of latitude for further exploration.
Probably the content in this book might be most relevant to people in grade 5 or 6 or so. Younger children may want to start with The I Hate Mathematics Book first. While the book does touch on topics that might be unfamiliar to students in those grades (such as exponents), it does a good job at describing them in a way that is both interesting and allows the reader to understand enough to appreciate the book.
Although my memory of things that occurred 25 years ago is fuzzy, I recall reading the book in grade four and having no significant problems understanding either the mathematics or the writing. However, I was good at both math and English. One potential issue that I see with the book is that it may not be a good fit for people who are good at math but not so good at English; in grade 5 or 6 or so, when the content might be the most relevant to them, they may have difficulty reading the book; when they are able to read the book, they may find the book to be beneath them. Unlike The I Hate Mathematics Book, many pages of this book contain lots of typewritten text, so there is a lot to read. Perhaps having an adult handy to assist with comprehension might be the answer. Despite this potential drawback, this is a great book for kids that has the potential to become one of their favourites.