It isn’t easy to convince children that winning isn’t everything when you consider how much emphasis is placed on winning in the media. As I wrote this answer, the winter Olympics were in full swing. All the attention was given to the gold medal winners, even though the winning margins were only fractions of seconds!
Some of the teaching about sportsmanship has to occur via modeling. Most of us, when playing with our grandchildren, will throw the ball a little wildly or deliberately strike out occasionally. That gives us a chance to lament good-naturedly, “I threw wildly that time, but it was fun, anyway.”
With indoor games that sort of “positive deceit” is more difficult. The next time your grandson has a fit if he doesn’t win, say matter-of-factly, “Well, that’s the end of the game tonight” and quietly put the game board away. If you think it won’t upset him too much, add, “Next time we play, I hope you remember that everybody likes to win sometimes, and there’s no point getting upset if you don’t win every time.”
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.