Might sound like an empty phrase, but it's about playing, not about winning.

Another thing: how will they ever learn to play better if all you show them is how you lose? I've played against kids like that. It's sad to see how they cannot grasp that they aren't going to win this time. Worse: when they think that bending the rules* to their advantage is part of the game.

But there's a delicate balance, too. If the kid loses all the time they might lose the joy as well.

When I play with kids I always show them what good tactics look like but sometimes, when it isn't too obvious, I seem to "forget" things for one move. Never bend the rules* though. If we talk about rule-based games of course.

* probably much less possible with video games.