For my 10 year old daughter and I, it's always been reading. We read together many nights, and she asks every night. She's so patient with me on those nights that I don't have the time, and of course I feel guilty every time.
For my 8 year old son, he's started to get into sports the last year or so. He has minor development issues, but he's come an incredibly long way. He's to the point that he can do anything, but probably won't ever be a star athlete. We put him in his first "competitive" (i.e. keeps score) baseball league this season. I assisted coaching, which eased my concerns. That said, I was an emotional ball of worry going into the season. I didn't want him to feel out of place with other boys his age, because I know how kids can be. It went incredibly well. He improved by leaps and bounds, coaches and kids were all great (some were really incredible little ballplayers), and they ultimately went undefeated. I lived and died with his every play. Highs and lows that I don't think I ever felt as I played sports as a kid. They eventually won their post-season tourney. Seeing him accept his trophy with a beaming smile......friends, it just doesn't get any better. I had to fight back tears knowing the things he's been through.
I have a 5 year old daughter who hasn't completely latched onto something yet. I think my "thing" with her will be swimming. This year she really turned into a fish. She loves going down the slide with dad, so that means I love to go on the slide.
I can't stress enough to take every chance you can to make memories with your kids. The last couple of years, I've really begun to take stock of my life. I suppose it's a mini mid life crisis, but I think every day about whether I'm living my life in such a way that I'll look back and feel good about it. Being a good father will be #1 on the list of those things I take stock of when that time comes.