What you can do is have them sit across from you with their legs open like a V. Practice rolling the ball back and forth. We have done this with all of them just make a circle and have everyone open their legs so they are touching the next persons foot. When rolling it around we talk about sharing and taking turns. "It is R's turn, T roll it R." "F isn't it nice that they are sharing". I think this reinforces it when they are pointed out the nice things they do are doing.