We've always called her "Little Nancy." Of course, that name fit when she was downy and new and weighed 6 pounds.

But the name stuck, especially because she was the third - and last - of our three daughters. After all, I was already in my late 20s when I had her, and in that era, women closing in on their 30s often didn't have babies. Somehow, we believed the myth that it wasn't healthy to do that.

So, yes, I cherished every moment that this last tiny being stayed . . . well, tiny. Every first was somehow not what it was with her sisters. "Nancy took her first step today," I wrote in her baby book with the pink satin cover. "I cried."

But Nancy wasn't about to wait until I was ready for her milestones. There are family jokes about how feisty this youngest daughter became, thanks to the audacious tutelage of her older sisters, who taught her everything from curse words to what R-rated movies were all about.

My protectiveness was doomed. I lost out to the wiles of Jill and Amy to make this youngest one precocious and sassy.

Most of my friends couldn't wait to get that last kid in school for a full day, but I would happily have stuck to what those friends regarded as the hellish half-days of kindergarten.

One of the first essays I ever wrote was about watching this last born marching off in the first-grade crooked line in her plaid dress and Buster Brown shoes. I knew the world would have her now.

The rest of Nancy's childhood was a blur. Of course, she seldom got anything new. She lived in a world of hand-me-downs, from her bikes to her camp towels to her bedrooms. As each sister left for college, Nancy would reinstall herself in the empty room. I dreaded the day when those bedrooms at the top of the stairs would all yawn empty.

I blush to admit that when Nancy left for college, my husband and I fled the country. We left on a trip to Scandinavia, not just because it was a place we'd longed to see, but also because it put a healthy distance between Little Nancy and us.

And I still left a trail of tears in Stockholm.

I'm sure a psychiatrist would say I felt that sense of loss because Nancy was my last legitimate hold on on-site motherhood, a chapter I loved. Or perhaps my attachment to her was a deep and deforming fear about my own aging.

I do know that those four college years allowed me to inevitably let this last daughter go. I knew it when we began the role reversals that come when our children begin to teach, counsel, and guide us.

And that has surely happened over these years.

The markers of her maturity came in a steady stream.

In college, Nancy met a man more perfect than any other - and she married him with our enthusiastic approval.

Little Nancy was a bona fide grown-up who got a doctorate and became the mother of three superactive sons.

But now, along comes another marker. One that has unexpectedly flattened me.

In a few weeks, Nancy Friedman Zinn will turn 50, the big 5-0.

Because I've already been there with her sisters, I know the occasion will be marked with a celebration, one that will somehow match Nancy's style: funny, irreverent, and sentimental, too.

I am now the mother of daughters, all middle-age.

Will they ever need me again? Or will everything reverse - they the wisdom-givers, I the needy recipient?

It's already happening. The emerging pattern is I ask, they answer.

I note that they call and email me more. And, occasionally, they fuss about why the same mother who encouraged them to join a gym should perhaps cut back on her own exercise routine.

Little Nancy also believes I should limit my carbs.

There are times these days when I drag out the baby pictures and the fading snapshots of birthday parties and images of three little girls at the beach.

And I lament the time wasted warring about hair and cut of jeans and messy bedrooms. I want that time back.

Last week, I dreamed about Nancy when she had a sprinkling of freckles across her cheeks. I was helping her into her snowsuit and she was holding on to my shoulders.

That frozen vignette of a moment has to date back 45 years, but it was more vivid to me than anything that happened yesterday.

Yes, soon I will have three daughters in their 50s. Little Nancy, too.

So why do I still feel the powerful, almost overwhelming, gravitational pull to keep them near, to keep them safe, and to love them beyond all reason?

I guess because I'm a mother.