There is something bittersweet about a last baby.

When any baby arrives, you know that she – and no other – was the person your family needed. Each child of any family, no matter the number, adds a new dimension, filling a space that was empty. But your last baby completes your family. She draws the final line of the cube; she is the last missing piece.

And while there is joy – and a measure of relief — to be found in this completion of your unit there is also a feeling of loss. Each milestone your last baby passes is the last milestone your family passes. Knowing this brings you a constant, often irritating, urge to feel the fullness of your time with your child: to burn the magical moments into your memory so that you never lose them.

On the other hand, that same urge to brand moments into your brain is also there when you are waking up every hour to nurse that last baby for seemingly endless months. It helps you “treasure” those less pleasant moments, like when that last baby turns two and finds the Sharpie you thought you hid, or when she turns three and you are carrying her kicking and screaming out of a store. There is a certain satisfaction in knowing you will never have to buy diapers again.

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Today, my last baby turns five and the yearning to be able to bring back her babyhood, to revive the time when I was everything to her has been strong.

But I’m not giving in to it. Because this last baby of mine is becoming a person I want to know better. The depth and beauty of her personality are just beginning to show.

She has spirit and charm and an irresistible spark of impishness. Her voice is cartoonishly cute: sweet, with a hint of rasp, and she uses it all the time. She notices things that other people don’t. She craves the comfort of her parents’ arms, and she hugs her sister with crushing love. She does nothing by halves. She is kind and curious and spectacularly bright. She growls when she is angry. She has brilliant blue eyes, but it’s in her smile that you can see her soul.

She is my last baby, and today she is five. In a few short months, she will start kindergarten, where the path to independence begins. The heartstring connecting us will stretch, steadily, irreversibly, as she comes into herself.

The urge to etch moments into my memory won’t go away. I don’t want it to. There are years of last moments — precious and painful and irritating and fun – ahead of us.