Recently, my two-year-old son and I were strolling down a sidewalk together. Both in our own little worlds, we hadn't spoken until I felt a tugging at my hand. Looking up at me, he exclaimed, "Run, Mommy, run!" Gazing back down at him, I almost had to laugh.

At six and one-half months pregnant, I can barely manage a quick walk, let alone a full-fledged run. Activities I used to take for granted, such as getting up from a chair without a grunt of effort, are things of the past. Even my family is shocked at the enormity of my belly. A friend likes to tease me about twins.

He tugs my hand more urgently and repeats, "Run, Mommy!" I start to shake my head no, but then I hesitate. How many times have I told him "no" lately?

"No, Nicholas. We can't play that rough-it could hurt the baby."

"No, I can't give you a horsey ride. You see, my back aches constantly now."

"No, Nicholas. I don't want to color-I just want to rest."

These months of pregnancy have been bittersweet. I deeply love this coming child and delight in every little nudge and kick. But it has occurred to me that this is the last time in Nicky's childhood that it will be just the two of us. Soon enough he will have to learn to share . . . Mommy's lap, Mommy's hugs, Mommy's attention.

Then I look, really look, at him. I study his outstretched hand, so pudgy and dimpled. I suddenly realize that one day it will be larger than my own. I look into his clear brown eyes, so free from our adult world of worries. They are lit up, in love with life and so excited. "Please don't ever grow up," I want to tell him. "Please always stay my little boy." He is so beautiful at this moment it actually makes my heart physically hurt.

I kneel down to his level. (Difficult, I admit, but I manage.) Then I take a moment to think at his level. We adults spend so much time worrying-about money, our careers, our responsibilities. None of this means anything to him. He is two, and he wants to run. With me, his mommy. This means something to him. And now it means something to me.

I grab his little hand tightly in my own. "Yes, Nicholas," I say. "I'll run with you." He waits for me to stand, and then we're off! His sturdy legs pound the pavement fiercely as I do my best to keep up.

It flashes through my mind that to other people we might look pretty ridiculous. A running toddler pulling his pregnant mother (who is by now huffing and puffing) along behind him. Nicholas looks at me with a huge grin. "Run, Mommy, run!" and laughs. Faster and faster we go. I am laughing out loud now, too. I forget about my aching back and my huge stomach. I forget about everything except how much I love my son. Though I lag behind, not once does he let go of my hand.

We finally do pass someone, a silver-haired lady! Instead of a strange look, she gives us a genuine smile. Maybe our joy is contagious, or maybe she remembers her own son at that age. Or maybe, just maybe, she sees what's really happening. While Nick and my feet are busy running, our hearts are busy flying.