What is the best way to teach a 6 yr old that losing in sports is a part of learning?

i think the best way to teach your child that losing is part of winning is to make them watch live matches. you could either take your kid to a live match nearby, or watch live recordings together. show your child how the losing sports person behaves even after losing out to the opponent. i'd say go for a recorded match so that you can see the reaction beforehand before showing your child. tell your child that losing a match is a way to understand what you did wrong, and you can always practice more, so that you are better in the next match. it may take some time for a 6 year old to understand, but it will happen eventually.