This coloring worksheet is meant for 5th, 6th and perhaps 7th graders. It is a little easier in that the individual valves are not labeled and there is some explanation as to what the individual parts do. There is also coloring instructions. I find that coloring as a labeling tool really helps kids remember structures. You can also ask them to trace a blood cell through the heart. Notice that the right pulmonary vein goes behind the heart and would open into the left atrium. It's hard to draw that without causing too much confusion.