This has been a big week in Toddler World. Since Monday, she has lived life without diapers. Sure, we’re still doing the Pull-Up thing during naps and nights. But still. This is big. Bigger than big. Suddenly, my little girl is not so little, occupying the precarious planet of panties and potties. (Apologies if you too hate the word panties. It’s just that I like alliteration more than I hate panties. Maybe. Yuck.)

For five days now, we have navigated the world of playgrounds and grocery stores without the snug safety of a diaper. For five days now, I have lugged around at least two breeds of portable potties. For five days now, I have chirped in Toddler’s ear constantly, asking her whether she needs to go “peeps.” For five days now, I’ve seen my girl through a new, heart-wrenching lens. My baby is suddenly, proudly, a little girl.

Yesterday was the true test. I dropped her off at her class at the Children’s Museum. On the way there, I explained to her over and over that if she needed to use the bathroom, she would have to tell her teacher. Over and over, she nodded. After getting her situated at the art table and reminding her one more time that I would not be around to escort her to the potty and handing over a change of clothes to her teachers, I left. Before walking to the coffee shop with my magical Mommy Friends, I looked back through that little glass window in the door at my little girl, intensely focused on her blue paint masterpiece. And as I walked away, I felt a profound pang and thought: Here I am, trusting her. Letting her go.

At the coffee shop, my Mommy Friends and I chatted and laughed, traded stories and sagas. Together, we marveled at how quickly the seasons slide by and how quickly our kids are growing up. Most of us have a second child, or one on the way. When we returned to the little classroom an hour later, anxiously, I peered through that same window. And I spotted Toddler. She wore the same pants. She pranced around the room, all smiles. I opened the door and all of us filed in. Toddler spotted me and hurled herself at me. In her tiny ear, I whispered that question I’ve asked countless times this week: “Do you need to go peeps?”

Mere inches from my face, she looked at me, rolled those impossible blue eyes, and said, “Mommy! I already did!” and then she skipped away. Away from me. I looked at her teacher who nodded and smiled. This was big. My Mommy Pals congratulated me on this milestone, on this step. One kid officially out of diapers! they proclaimed. I thanked them. Effusively, I thanked the teacher for taking care of my girl. Effusively, I told Toddler how proud I was of her. Because I was. I was.

And yet. On the stroll home, I looked down at her, the suddenly long and unruly tangles of hair, the long legs kicking, almost grazing the sidewalk. And I suddenly thought, she’s not going to need a stroller much longer. Over and over, I told myself how proud I was of this potty training victory. And over and over, I kept telling her this too, six words trite and true echoing from my lips: “You are such a big girl!” Because she is now.

But behind my big old sunglasses, behind that surface pride, a swell of sadness built. And a single memory was suddenly crisp in my mind. New Year’s Day 2007. Her first day. When Husband and I, blind with exhaustion and shock and love, hunched over that tiny glass bassinet while a kind nurse taught us how to change her diaper. How to fold down the top part to avoid the umbilical cord. Block by block, I walked, looking down at my big girl and remembering my baby, marveling that they are indeed one and the same creature. Block by block, I finally realized just what these milestones are. They are bittersweet goodbyes.

So, this week it was goodbye to diapers. For whatever reason, I am not overcome with relief. I am proud, yes. Fiercely proud. But I’m also a bit sad.