There are tons of fabulous children's books out there that allow for excellent cross-curricular activities. An engaging read aloud followed by a math activity is a great way to have your students fall in love with both math and literature!
The Greedy Triangle, by Marilyn Burns, is one of my personal favorites. This triangle just can't make up his mind about how many sides he should have. Three is obviously not enough, four is inadequate as soon as he sees a pentagon, and then a hexagon appears and he is again dissatisfied. It's an excellent way to teach geometric concepts to young children. (And with such a greedy three-sided protagonist, this book provides a nice way to sneak in a social skills lesson.)
Valerie Flournoy's The Patchwork Quilt is one of several children's books in which quilting plays a large role. Quilting is a great way to again teach some important geometric concepts. Start with symmetry and tessellations and go from there. If you decide to follow up this story with a quilting activity for your students, you'll appeal to some of those hard-to-reach students with a hands-on activity that involves cutting, gluing, and creating paper patterns. Make those reading and math connections often, and you'll be showing your students how creative numbers and shapes can really be.