Last summer, my son was away with relatives when my daughter received an unexpected invitation to spend a few days on Cape Cod. Buoyed by the notion of being footloose and kid-free, I helped her pack, cheerfully throwing items into her overnight bag. When her ride pulled up, I pushed my girl into the back seat, kissed her goodbye, and stood in the driveway waving until the car rounded the corner. Then I turned back toward the empty house. I didn't know what to do. At that moment, I realized that my children make up the framework of my life. They give me purpose and structure. Without them, I was aimless. All of my fantasies of kidless self-indulgence evaporated in a puff of exhaust from a beach-bound minivan. And for the next 72 hours, I drifted like a ship cut loose from its anchor.

A few days later, the kids were back and our home was again filled with the sounds of bickering and sniping. I struggled to remember why I had missed them, but I couldn't. The daydream of being childless and whooping it up in Rio crowded out all other thoughts.

Until last week. I was working on the monthly PTO newsletter when it occurred to me that in June my daughter, a 7th grader, will leave the school she's attended since kindergarten. The enormity of it hit like a medicine ball to the stomach. Not only will she be at the high school with—this is where I hyperventilate—teenagers; I also won't be in the PTO anymore.

I've been part of that group for years. I go to meetings. I faithfully volunteer. I patronize fundraisers. I've been proud to contribute to an organization that accomplishes so much for the school. Who will I be if I can't identify myself as a member of the Miscoe Hill PTO? True, my son will be moving up to the school in a couple of years, but by then there will be a whole new board and membership. It won't be the same. Quite frankly, I've become attached to the PTO. I'm not prepared to be kicked out of the club.

But that's what happens when your kids grow up and move on. They pull you along with them, like it or not. Parenthood brings with it exclusive membership rights. When my kids were babies, they were my admission to play groups. As they got older, they opened me up to scouts, gymnastics, band, piano, baseball, and, of course, the PTO. The rhythm of these activities has become as familiar to my family as breathing. When you're living it every day, you forget that it's all temporary. Until your membership privileges in one of the clubs is revoked. The kids outgrow scouts, they give up band, they graduate from school. Or they simply take off for a few days in the summer, leaving you directionless and disoriented. As with any ending, you're left with no choice but to accept it and move on.

Maybe these small losses are preparation for the big, inevitable one, when the kids leave home for good. Hopefully, by the time my kids don't need me anymore, I will have replaced my hands-on involvement with their activities with new interests to give my life structure and purpose. But for now, I'm not going to worry about it. When my daughter goes up to the—pardon me while I hyperventilate again—high school, I'll be right there with her, seeking out the parent group. My daughter might argue that she's already at the stage where she doesn't need me anymore. But that's not the point. I still need her.

Sharron Kahn Luttrell volunteers for parent groups at two schools in Mendon, Mass.