When you hear the sound of your youngest child’s seatbelt buckling without assistance you know you’ve entered a new stage of motherhood. That click was just one of several independent moments in the past few weeks that are bittersweet reminders that our little family is progressing along. It’s also additional evidence that the baby care phase of motherhood is pretty much a part of my past. I’ve known since the day my youngest daughter was born that she would be my last, so I’ve tried to cherish all of her stages. (Let me tell you there’s not much to cherish in the tantrum phase.)

My youngest daughter has given up her “floaties” for the pool and has become an independent swimmer. She doesn’t just doggie paddle or hang onto the edge, either. She jumps in off the side while shouting “cannonball!” and leaves a wake of foam behind her. In fact, as she took her maiden voyage she pushed me aside and said words that I’m sure will echo in my mind for the rest of mortality, “I don’t need you anymore.” While it’s exciting to see her move ahead in her independence there’s a portion of me that aches a little inside for those days when we snuggled up in the rocking chair and she’d fall asleep in my arms. Don’t get me wrong, though, I don’t miss the endless nights of no sleep or the constant diaper changes.

Today marks her fourth year of life and it really does amaze me how fast time does go. It seems like just yesterday I held her in my arms in the hospital and she grabbed hold of my index finger and looked in my eyes as if to say, “Hi, old friend. I’m finally here with you again.”

When my older girls were babies, it felt to me that time stood still. Every day was the same. It was like watching a mommy–narrated version of the movie Groundhog Day. Those were some of the hardest years of motherhood I’ve ever survived, but now as I see that door closing, I can truly see how that old cliché is a valid one: They do grow up so fast. I’ve heard it a million times from strangers on the street and from my own mother, but now I’m living the cliché.

My oldest daughter turned nine last month and I realized her time under our roof is half over. My other daughter is almost to the same mid-point. I have friends who have teenagers. How does this happen? When did we get here? Was there an off-ramp that I missed while I was in the fast lane? Was I too busy making peanut butter and jelly sandwiches to check my email that alerted me to a life change? It just feels like it all happened so quickly and without warning.

Really, though, the warnings have been there all along. I’m grateful we celebrate birthdays and other important milestones to serve as reminders that time is a precious commodity. Once it is used, it can never be returned.