One identical preschool-aged twin said to his brother as they splashed in the bath, "Am I just like you?" His brother answered, "No, I have a boat."

My two oldest daughters, identical twins Liza and Hallie, are 7. They've always been each other's best friend, and they've remained inseparable for most of their young lives. They play together, they're never far apart from each other in school and they love taking extracurricular activities together like tap dancing, art, gymnastics and choir. Is there much rivalry between them? Yes, they have their moments.

When they were younger, say 3 to 5, it was the simple things that could set off one being envious of the other, like running an errand with Mommy or going outside to get the paper with Daddy. If one errand was, for whatever reason, more popular, the envy was greater.

Although I love to do things together as a family, sometimes being apart from each other is a practical necessity as well as being a good thing for the girls. It forces them to develop their own interests rather than making decisions based on what their sister does, wants or thinks.

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