You guys made the point I was going to. Karting is considered the premier training activity for most kinds of race driving, at least for smaller, more agile cars like formula racing. Top drivers continue karting to keep their skills fresh.
As to being a waste of money for kids, there's a point there. As with music education, the probability of eventual professional success is quite low. I'm sure more people make a living in music, and the aggregate money they earn is probably far greater than with motor racing. In both the top people make millions, but there are far more top people in music clearly. And racing is far more expensive to progress in. since in many series you have to basically buy a faster car than your competitor. "Anyone can afford to go racing. All it costs is all you have." And you better dominate each series to get noticed.
If this is what westcoastsoloist meant, he has a point. But karting doesn't have to get too expensive and does teach many good values and confidence, etc. All things in moderation.