One afternoon about six years ago, Hallie, the second of our four daughters and also a twin, decided she had had enough crawling and stood up to walk. Down the hallway she went, teetering like she had had one too many drinks, determined to get to the end. She made it about halfway and plopped down, apparently satisfied with her short journey, then looked up at the cheering audience and smiled. That's when Liza, her older (by 11 minutes) identical twin sister decided it was her turn. And off she went.

That's how Liza and Hallie have done things since birth. They rolled over, crawled, walked and even got their first tooth all within minutes of each other. They've taken turns being the "first" on the physical milestones as well as in other ways. Maybe Liza will like art for a few weeks and then it's Hallie's turn. That's when Liza decides she wants to do what Hallie was interested in – maybe dressing up or playing soccer.

But whether it's something social, academic or physical, they're never too far from each other when it comes to the way their minds work. They're 7 now, and they've never been more than 1/2 pound different in weight or 1/2 inch in height. And they've always been each other's best friends.

They started preschool together two mornings a week when they were 2, then three times a week when they were 3, always in the same classroom. But when they turned 4, my wife and I decided it was time to consider placing them in separate classrooms. The preschool they attended doesn't have a separation policy for twins but we felt it was time for Liza and Hallie to grow more independent of each other. And despite dressing them differently from an early age, many people still got them confused since they looked so much alike. We wanted to make sure that others got to know them as the individuals that we knew they were.

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