I have always told my kids. "I like watching you play."
Sometimes they would ask me how they did. That sounds like a chance to critique the game. But really, does anyone want to hear what they did wrong after playing a "game" that's meant to be fun?
I found after a few mistrials, that saying that I liked watching them play, put a smile on their face. They would relax and off we would go to the next thing on our agenda.
My daughter was real tough on herself when she was young. It was important to me, that I took pressure off, and let it be a game. She continued on to play three sports in high school. She went to the final 16 in the State Playoffs four times in three sports.
She still plays softball today and flies around the country to do that. I play softball with my son James, a team of 30 somethings. Yeah, they still let a guy in his 60's play with them. It's my job to joke around with the other team so that the games don't get so serious.
If you're a parent, or a husband, it's so easy. Just say you love watching them play. They will love you for that.