I always like to review the concept of one half when we are ready to begin fractions in third grade. There seems to be a handful of students who really don't understand what it means. A few months ago I decided to look for a book that would help, and came across one in my favorite "MathStart" series by Stuart J. Murphy.
When we start back after Christmas break I plan to share this book with my classes to begin our discussion of fractions. It is a story of a brother and sister having to share a lunch. Sharing with a sibling is a common experience, so students will be able to relate the concept of "one half" to real life.
I blogged about another favorite book, The Doorbell Rang, here. When we begin fractions that one also comes out and we look at it differently -- instead of division, we talk about the fractional part of the cookies that the kids are sharing in that story.