As of today, my son Finn has officially been in the world for four years, just forty-eight months; I have had car payments that lasted longer than this. I was in college longer than this. His whole life has spanned the length of a presidential term, and yet, his presence inhabits my world so fully, I simply cannot imagine any world without him in it.

Motherhood keeps knocking me upside the head with how much it has reoriented my heart.

Yesterday was exactly one week since Finn joined his sister at "big kid school". He is the youngest student in a school that goes all the way to the sixth grade; Finn still has the distinct whiff of diaper cream on him and yet he is rubbing elbows with boys on their way to needing aftershave. It is a delight and a confusing sight to see him here: he is a hit. Everyone loves him and he them, especially the older kids. "Hey, Finn!" the ten and eleven-year olds call to him, patting his little hooded sweatshirt, his 4T pants rolled up so they don't drag on the ground behind him in the cafeteria. He swoons over the girls twice his height and tries to match the stride of the big boys, joking with them, teasing them, and they return his affections in that way that boys do, making crazy faces and grunting like small mammals, which they are. Everyone is pleased with this situation, save Finn's sister, my sweet girl and soon to be seven-year old, Reese, who is completely mortified by the antics of her little brother. And, in addition to being mortified, is also, loving and worried and overprotective. She tells me lunchtime is stressful, at least for her; Finn won't eat enough and he keeps raising his shirt up and dancing at inappropriate times. She doesn't know if she's up to the challenge of maintaining the force that is Finn. And I tell her, she doesn't have to; there are teachers there, aides and helpers, all she has to do is be his sister, his friend, but she looks at me as though I have no idea what I am asking of her. And maybe I don't. Or maybe I do. To love Finn is a full-time job, even for Reese, I guess.

Like yesterday, when I picked them up from school. Reese was in her class getting her things and Finn and I were in his; he wanted to show me his art work but as he went to turn on the lights in his classroom, he accidentally set off the fire alarm instead. It was instant: the deafening sound, the blinking lights, the kids running all throughout the school thinking there were flames brewing somewhere behind them. At the moment his hand hit the panel, his panicked eyes flew to mine and then he was on me, his head buried in my shoulder, the tears flowing: "I'm so sorry. I'm so sorry." He would repeat it over and over as I ran out of the room carrying him, trying to flag down a teacher to explain, chaos rampant, lines of kids forming the way they'd been taught to in the countless drills they'd practiced. Finally I got the word through that it was a false alarm, but no one could shut it off; the lights and sound continued as Reese made her way to me, clutching her homework and lunch pail, her face confused and scared. I explained what had happened, but she couldn't comprehend it; her do-everything-by-the-book self could not process this huge misstep of her best friend, her shadow.

She'd left him alone, with me, for a moment and look what I'd let happen.

Everyone would think it was her fault. That he was bad. Worse, that she was. The entire evening was spent discussing that Finn is only, just barely, not even quite four and that people understand that accidents happen.

Finn would pipe in intermittently with "accidents happen, Elmo always says."

And then Reese would say, "Finn, this was not THAT kind of accident."

But today was better; I picked them up and we did not set off the fire alarm. Reese reported that he'd eaten his lunch and hadn't flashed anyone the entire day. Finn announced that Reese will get the biggest cupcake tomorrow because she is his bestest friend and her smile told me that she believed him, that she agreed. That she deserved it and more.

This boy, this girl. How lucky I am. How very, very lucky.

Happy birthday, my darling Finn. You are fabulous. I love you madly.