Play therapy is actually a really great technique that is used with younger children that may not be able to tell you what is going on. I have studied this im alot of my child development classes. Basically they just set up a room with lots of different toys in it for the child to play with and the psychologist or several psychologist observe the child to see how they are playing and what toys they are playing with. And by doing this they are able to tell what the child is thinking, by the way that the child plays.