Dear Mary,

So here we are, the last night of your first year. As I'm writing this, you are about eight feet away from me on your mom's lap. You've just finished a last little snack before bedtime, which is part of your normal routine. Unlike most nights, though, we're in a hotel room more than a thousand miles from home—your first trip to another country. It's funny for me to consider that with you, I'm going to be seeing a lot of firsts for the last time. But I'm glad that you're the one I'll see them with.

Before you were born, your mom and I thought we knew what we were doing as parents, and we thought we knew what to expect from you. But from your very first day, you have demanded to be reckoned with on your own terms. You are strong-willed and determined. You are a girl on the go. Today, for the first time, you decided to stand without holding onto anything for balance. I'm sure it's only a matter of weeks or even days before you take your first steps. None of your family is surprised about this; you have always had places to go, things you wanted to be doing, and you are not one to let anything stand in your way. It's a big world out there and often a tough one; I think your grit and drive will serve you well as you continue to grow and find your way.

You're sometimes a handful, and sometimes a sweetheart. You're goofy, like your brother and sister—you love to make people laugh. You're little for your age when it comes to height and weight, but like you might hear in stories about another adventurous soul, you're bigger on the inside.

Tomorrow is your birthday, and you are going to be surrounded by family celebrating your first year. For you, I think tomorrow is going to be no big deal, maybe just something you'll see pictures of when you get older. For me and your mom, though, it's a pretty big deal: you're one year old, and you're the one who's made our family complete.

I hope you have a great day, baby girl. I love you.

Dear Jason,

Every year I write you a letter and make a video for you. In a lot of ways, what goes into these letters isn't much different from what I do every day: I think about you, what you're like, how you've grown, and how much I love you. Lately, too, I've been thinking a lot about what kind of man you will be when you're grown up, and what the world will be like when you get there. A lot happens out in the world, some of it good and some of it bad, and sometimes I worry about the problems you will face some day. But more and more I am comforted by the ways that you show me how good a person you are. You make me very proud to be your dad.

In just the past week, two different families have commented to me and your mom about how polite and mature you are. And it's true: sometimes life gets frustrating, but you are really good at talking things out, and you care a lot about doing the right thing. This year you became a big brother for the second time, and you are so good at taking care of your new baby sister. You play with her and you talk to her. You're just a great brother, to both of your sisters.

Another big step for you was earning your junior black belt, after two whole years persevering and learning in your karate class. I've gotten to come visit your class more often this year, and I love to see how good you are at focusing and improving your skills.

But most of all, I love that you're fun and funny. After we went and saw Inside Out, I've liked to say that you live on Goofball Island. In fact, just as I was writing this letter to you, you came and joked around with me about boogers, and also tried to tickle me. (Your mom doesn't like the booger jokes as much, but that's OK. This can be our thing.) I like that you're playful and enthusiastic, and I hope that never changes.

Tomorrow is your birthday, and I'm taking the whole day off work so I can spend it with you. It's going to be a great day, I know it. Happy birthday, pal.

The thing that strikes me the most about this picture is not how much different she looked then, nor how much the same she looks now. It's not the way she still sometimes sleeps with her arms raised and hands in little fists. It's not even the swiftness with which the past eight, nearly nine months have passed. All of those things do cross my mind when I look at this picture, but mostly what amazes me is seeing her at 6:10 in the morning, sleeping soundly enough for me to take her picture—or even enter the room—without waking her.

Child, I love you very much. I love your energy, your inquisitiveness, and your impish little smile. I love that you are motivated, that you go after what you want, and I hope that you stay that way when you are older.

But please, at 2:30 in the morning, this is the only thing I ever want to see you doing.

Lately when she calls out in the night, it's for Mommy. When she needs help in the bathroom, her voice rings out down the hall, "Mommy!" When she wakes up in the morning, her first request is Mommy. Sometimes she gets me instead, but she just sets her jaw and frowns. "No," she says, "I want Mommy."

I'm not sure exactly what it was she was writing here—the title of her next show, most likely—but I think I see "Daddy" in there. It's nice to know that she thinks of me sometimes.

March, two years ago. She was a year and a half old, running, climbing, playing on a cool Easter morning on a huge backyard lawn in Virginia. The breeze on her face made her squint and squeal with laughter; it's something she's always loved, which she has in common with me and her sister, but not her mother or brother. She's bigger today but so far she still fits in my arms. Sometimes when I pick her up I still like to blow into her face, and her eyes sparkle and her manic little giggle warbles, she takes a breath to blow back at me and I quickly blow again, a little puff into her open mouth and she shrieks in delight, covering my lips with her hands and blowing back, blowing back, blowing back, her breath still sweet as a baby's, her joy still just as radiant and unguarded.

He really started noticing the camera when he was about three. That is, he'd seen it before, but that's the age when he really started to understand what it meant, and that I was looking at him. I don't know that it was self-consciousness, exactly, though that came too, eventually. But sometimes he didn't want to play along, and so he began to hide himself. He would duck his head down, or sometimes simply close his eyes in protest. Back then, it came with a scowl.

That was when I started asking his permission to take the pictures.

Nowadays, he will agree or disagree to being in a picture. Sometimes he will come along grudgingly, sometimes with enthusiasm. Sometimes not at all. Just before I took this picture, I told him that the light was really nice, and asked him if he would sit up so I could take a picture. He said OK, and closed his eyes. I asked him if he was sure it was OK, and he patiently said yes, so I clicked the shutter.

Shortly afterwards, a mischievous grin stole across his face and he pulled his pants down, shoving his back side toward the lens. "Take a picture of that!" he shouted gleefully.

So I did.

He said it was his favorite picture ever.

Juliette sometimes looks at photos and says that his feet look like mine. His toes haven't quite lost that round, chubby, baby toe-ness, not yet. But his feet are getting longer and narrower.

Last night he decided that he wanted to take a shower—I think he was tired of waiting for his sister to finish her chores. He doesn't do this often yet, but he will. And then this kind of picture—of which I must have hundreds—will get fewer and farther between. The girls will still be taking baths for a while, of course. I suppose that softens the blow a bit, but each child is an individual, and parenting each one is its own story. Having younger kids doesn't really make me miss the oldest's littleness any less.

"Dinner is just about ready," I say. "It's time to clean up and come inside."

"OK!" she says.

A few minutes later I return. She is stooped over in the middle of lawn, picking up leaves one by one. The yard is still littered with toys.

"Eve, come on," I say. "You can play with the leaves some other time. You have to clean up and come in to dinner now."

"No! I'm not playing!" she insists. "I have to put the leaves in my collection!"

Around the corner, next to the crowd of tricycles and scooters, lies a little pile of yellow and green, fading to brown. She crouches down and places the leaf in her fingers right in the middle.

"Is that your collection?" I ask.

"Yes," she says. She's so proud.

I don't know why fingers get wrinkly when you've been in the pool or the bath too long. I don't know why she wants to wear her goggles in the pool when she refuses to put her face in the water. There are lots of things I don't know. That's just how it is.