If I have learned one thing as a father and a grandfather, aside from the important fact that maturity is best left to young people, it’s that kids grow up fast. This is what happens when you feed them. And if you think your kids grow up fast, wait until you have grandchildren. That’s what my wife, Sue, and I discovered when we visited our older daughter, Katie; her husband, Dave; and their children, Xavier, Zoe and Quinn. We hadn’t seen them in 10 months. And before that, we hadn’t seen them in a year and a half. Considering Xavier is about to turn 5 and Zoe and her twin brother, Quinn, will …