I've done an enormous amount of kart racing, loads of fun. The way the track rules are set up at the places I run at, it's never made sense to buy my own, but it's definitely a more social and family-friendly sport than actual car racing. When I lived in DC, I'd do company "team building" events at the local kart track -- 50-70 people doing a 3-5 race competition followed by grilling and hanging out in the parking lot. I was typically out at the kart track with a group of friends at least once a month, typically followed by burgers 'n' beer back at my place.
Compare that to racing my car, where I go and do the thing, hang out with the other racers, but only see them once every few months, so it doesn't really become a social thing so much as just a thing that I enjoy doing. None of my "normal" friends can afford to get into racing, so I don't take my friends to track days. The groups I run with don't generally approve of passengers, so I can't take a date to the track in my actual car. Or, I guess I could, but she'd be stuck in the pits all day, so that's really not much fun at all.
Add to that the fact that karting allows actual wheel-to-wheel racing without the risk of wrecking my actual car, and you've got a recipe for a lot of fun for not a lot of money. I do think that actual car racing is a better experience -- it's more challenging, more nuanced, and generally more fun. But it's also a much less social experience for me.
For kids? Karting is AWESOME. Get 'em started young. Even if they don't turn out to be race car drivers when they grow up, they'll learn a lot about how cars handle and how to manage complex situations on the pavement. I absolutely plan on taking my kids racing, when I eventually have kids.
