My Five Year Old Grandson Has Started To Play With

My five year old grandson has started to play with his poop. He has no mental problems, he just started pre gindergarden. Just in the last four weeks he has started smearing his poop on the walls and toilet seat. My son and his wife are very concerned. They have made an appointmet with his Doctor. I was wondering do many children do this. I had four children and never had this problem.