Personal experiences as an elementary school math resource teacher and a 1st grade teacher have led me to believe that mathematics learning should be engaging and fun at any level (including the graduate level), but clearly it is of the utmost importance to effectively engage students at an early age, so as to hopefully instill in them a lifelong appreciation for the subject. Most children are quite active in nature, so providing hands-on activities that keep their minds and bodies actively involved is an important task. It seems that geometry is like the fail-proof mathematical concept that can pique the interest of even the toughest audiences. Probably because geometry is naturally hands-on and therefore easily applicable to real-life situations. Children can see and touch geometric concepts. It may seem trivial to adults, but numbers and number systems can in reality be quite abstract concepts to wrap some little brains around.
Another way to engage children is to give them a sense of ownership in the mathematics learning process, providing them with a keener awareness of mathematical applications, and thereby providing them with a more personal encounter with learning mathematics. Children feel empowered when they are permitted to study things that are of interest to them. Mathematical connections can be made to just about anything that children find curious in our present day society. Be it the arts, dance, music, video games, computers, ipods, facebook, twitter, sports, or games, organic "aha" or "teachable" moments can easily be generated by harnessing children's intuitve curiosities.
I have found literature (specifically picture books) a useful tool for harnessing some of these curiosities in children of all ages. Additionally, actively listening to a narrative can engage the mind and promote purposeful thinking, learning, and even critical analysis.
Anyway, another reason that I enjoy using literature to teach math is that literature tends to provide a portal for asking and generating thought provoking and meaningful questions. One can kind of let the narrative guide the instruction. If the kids aren't interested in it, there is no point in belaboring the issue, so move on until you find a piece of literature that does interest them. Some books that I would recommend (based on student ratings) are The Very Greedy Triangle, The Number Devil, Anno's Mysterious Multiplying Jar, Amanda Bean's Amazing Dream, The Grapes of Math, How Much Is a Million, Sir Cumference and the Dragon of Pi, The Best of Times, One Grain of Rice, Spaghetti and Meatballs For All, and we can't forget how Lewis Carroll's Alice in Wonderland is densely saturated with mathematical concepts...There are oodles more! However, authors that I tend to come back to on a consistent basis are Greg Tang, Jon Scieszka, Marilyn Burns, Cindy Nueschwander, and David M. Schwartz.
At the end of the day, just try to find ways to make mathematics learning engaging and thought provoking but also meaningful and fun! And by all means, one doesn't always have to use a mathematics picture book to teach math concepts. Once I read, It's Pumpkin Time, a book about the life cycle of pumpkins to my students and ended up creating measurement activities that corresponded with the book rather than science actitivies. Just get creative! Children love that!
More resources if you're interested.