Losing is a very normal phenomenon in chess, especailly for beginners. If one doesn't lose, one will not progress. There is definitely no need to worry. It's same as a baby learns to walk. S/he would fall down a lot, but s/he will also stand up again. What you need to do is encouraging her/him to try again. No judgement, just encouragement. You don't comment that s/he falls gracefully or clumsily. You don't laugh or scold. You just ask her/him to try again. Very natural. Nothing fancy.
Same should happen in chess. When your child loses, give her/him a hug. Tell her/him there will be another game, another tournament. S/he will win another day. Come back and try again. Commenting is useless. Leave that job to her/his coach. Believe that our kids all want to win. They did their best. They will try again and do better.
Soon he will stop crying, and soon he will start to win.