The best way that I have found is that after the match find out why they were crying and most of the time they will say because I was hurt. I would ask them were you really hurt or were your feelings hurt because you were losing? Guess what 97% of the responses were. Because I was losing. I would then tell them that instead of crying use the tears for energy instead. It may sound cheesy but it works almost every time. I had a 6 year old come back from 11 down to only lose by one on a very close time expired in the third period call. He stood up and got loose just as the wistle blew but he never cried after the match he walked off the mat with his head held high and very tired from leaving everything on the mat.