I’m nursing the baby before bed, like I do every night, in the rocking chair that used to belong to my mom. My daughter, 8 months old, is wearing her cozy jammies with the lemons on them. Her soft head rests on my arm, and her little hand plays with my shirt, my thumb, my hair, and her own ear as she nurses. She’s tired. It wasn’t a particularly big day, but I think she’s hitting a growth spurt. She’s been extra hungry and sleepy (and clingy and fussy) for a few days.

She starts to doze off, and eventually I can tell she’s not eating anymore and she’s just nursing for comfort. I didn’t catch the moment she stopped looking for food and started looking for snuggles, but it doesn’t matter. I want to savor the weight of her warm body in my lap, cradled in my arms, half-asleep and perfectly content. There isn’t anything particularly special or unique about this moment. She and I have nursed together in this rocking chair many times since the day she came home from the hospital as a tiny newborn.

Maybe it’s because this moment is so ordinary and so peaceful that I want to bottle it up and keep it forever.

I hear the toddler running around out in the living room, and I hear my husband scolding him for pestering the cat. I can hardly believe the rambunctious boy, who will be three in just a few weeks, used to be the baby in my arms, nursing before bed in this same rocking chair. He used to fit across my lap and hum while he ate.

When did he stop being a baby and turn into a toddler? There wasn’t a ceremony to celebrate my son’s graduation from babyhood to boyhood. I don’t know when it happened, even though it all unfolded right before my eyes. He took his first independent toddling steps the week he turned 10 months old, in a rental house within earshot of the ocean. He said his first word, “cook,” as he watched Grandma in the kitchen. There were chocolate cupcakes at his first birthday party. When I gave him his first haircut to get rid of the messy mullet on the back of his head I remember thinking he looked so grown-up, but I didn’t feel as sad about that as I expected.

I don’t know when I transitioned from “new mom” to “toddler mom.” I only know it happened, and as I gaze down at the sleepy baby in my arms, I know it will happen again. Soon she’ll be the wild toddler thumping around the living room.

I take the baby off my boob and sit her up in my lap, snuggled against me, so we can read a book and say our prayers before she goes to bed. I put her in her sleep sack, switch on the sound machine and turn off the lamp, and hold her close while I sing her bedtime lullaby. As a newborn she loved to be held upright, pressed up against my chest, her tiny head resting where she could hear my heartbeat. Her whole self used to fit curled up between my collarbone and my belly button. Now she lays her head on my shoulder and her feet dangle down past my waist. She’s so big, and I can barely remember when her brother was this small.

Pacing around the dark nursery, I can only hear the sound machine, my own singing, and the baby’s soft, sleepy sighs. One day (probably soon) she’ll take her first steps. She’ll say a real word and mean it instead of just babbling “Ah!” and “Bababababa.” We’ll celebrate her birthday and I’ll let her hair grow. (Hopefully it comes in nicely so she isn’t stuck with either a mullet or a haircut that matches her brother’s.) She’ll get bigger and taller, and her face will lose its babyish roundness. Someday I’ll look at her and realize she’s grown into a little girl.

“Good night,” I say gently to my daughter. “Mommy and Daddy love you. We’ll see you in the morning.” I kiss her soft forehead and set her down in the crib—the same one that used to belong to her brother. She rolls onto her side, and I quietly slip out of the room.

I hope the growth spurt passes quickly. I hope she sleeps well tonight. I hope I always remember how it feels to cradle her in my arms.