Measure objects to the nearest unit and plot your measurements on a line plot. You could have each kid measure the length of their pencil, then plot the lengths together for the purpose of a lesson.
Watch these Khan Academy videos:
Conclude by leading this investigation:
2.MD.D.9: Generate measurement data by measuring lengths of several objects to the nearest whole unit, or by making repeated measurements of the same object. Show the measurements by making a line plot, where the horizontal scale is marked off in whole-number units.