If a child is playing sport, the emphasis should be on having fun. However, I believe learning that sometimes you lose is just as important.
There is a school of thought that if children are playing for fun, they should not keep score, which seems a bit backwards to me. Participation is great, especially in a country like New Zealand which struggles with obesity, but let's also give them a goal to chase.
Sport has winners and losers, that is a crucial part of it's make-up. I believe the greatest joy you can get from sport is when you dig deep and produce a win, when you and your teammates work together for the desired result. If there is no desired result, what is the point?
Admittedly, I am a competitive person, but I don't think you're ever too young to start learning that putting effort into something can result in reward. I'm not saying winning should be the be-all and end-all of the experience for children, but it should at least be an option.
As the old cliche goes; without the rain, we would never appreciate the warmth of the sun. Sport is like life - it is the failures and losses, that make success and victory so sweet.