We have a weather graph that we add to daily at circle time. We used heavy poster board with 5 different types of weather that we regularly experience in our area. The "meteorologist" (vocabulary word!) makes a forecast (another vocab word) which is of course a guess and velcros a small square symbol into the appropriate column on the graph. We count the numbers of different types of weather, observe how high the columns go, and talk about how our graph helps us see what kinds of weather we've had the most and least of. If we focus on an author for a week, Dr. Seuss for example, we will also make a graph showing the five major books read at circle time and at the end of the week each child will place a square representing their vote for their favorite book, and we will review the graph to see what book had the most fans. These activities introduce the concept of graphing so that they understand what it is. These activities are teacher directed and not open-ended, but graphing is a subject they will not understand unless it is taught first. You might want to introduce it that way, then provide the materials for them to experiment with making their own graph. Sounds like a great small group time activity!