Almost as soon as our son was born, we got these words of advice from friends and family with older kids. 'Try and enjoy every minute of it, because the days might feel long but the years will go by quickly.'

I took the advice to heart. I was in my 40s when I became a mom — time already felt precious. My pregnancy hadn't been easy. Serious complications in the third trimester had forced my son into the world six weeks before his due date. So, by the time we brought our tiny 4 pound 9 ounce preemie home, I was determined to enjoy every minute with him.

I wanted to remember each precious detail — his scent, the little animal sounds he made in the early weeks, the first time he rolled over and all the other early milestones. I hoped that by laying down these memories, I could slow down our time together, so the years wouldn't fly by quickly.

Thinking back, I did succeed somewhat, but only for brief moments.

For example, when he flashed his first voluntary smile at my husband and me, it felt as if the seconds expanded into minutes. I had the same experience the day he turned 2 months old, when we bathed him, weighed him, and heaved a collective sigh of relief because he was no longer the skin-and-bones-preemie, but a healthy, chubby baby. Then there was the time he first army-crawled, elbow by elbow, out of his nursery, months before he learned to do the real crawl.

And yet, now that he's nearly 3 years old, I look back and wonder: How did those months and years go by so quickly? How is my baby already a walking, talking, tantruming toddler, who tells stories and jokes? And on the days that he says things like "leave me alone," or "give me space," I can't help missing my sweet, cuddly baby.

The science behind sweet, in-the-moment 'baby-time'

Is there a scientific explanation, I wondered, for this shared experience of in-the-moment baby-time? And why is it that even when we parents do manage to make time slow down in the moment, the years still go by so fast?

It turns out, researchers say, it's because our brain's perception of time is fluid — determined by the kinds of experiences we have and how we experience things in the moment.

"We don't have a single perception of time," says Peter Tse, a neuroscientist at Dartmouth College. "We have a perception of time in the moment — perceptual time, you might call that. And then you have how you regard time by looking through your memories."

To make a lasting memory, pay attention

The brain perceives time based on how much information it is processing at any given moment, he adds, which in turn depends on how much attention we're paying to what we're doing and what's happening around us.

"If you're paying attention, you're actually processing more units of information per unit of objective time," says Tse. And that makes time feel subjectively longer.

This can happen when we are in a new place, absorbing all the little details around us. It can also happen when we're having an emotionally charged experience.

"So, if you're driving and you're skidding and about to hit the back of a car," he explains, "it seems to go in slow motion because suddenly your brain's processing tons of information and you're fully attentive."

The same applies to the pleasant, emotionally-engaging moments we share with our kids.

On a recent morning, while walking my son to his daycare, I noticed that the grass on the sidewalk and the field across the street were covered with the first frost of the winter.

I was so excited to show this to my son, that I forgot we were running late. We stopped so he could touch and feel the thin silvery layer of ice crystals on the grass and dried leaves beneath our feet. It was his first time encountering frost and he was awe-struck.

I don't remember how long we stood there as he picked up leaf after leaf, gently touching the frost with his fingers, watching it melt, asking questions. But I do remember that, for me, everything else zoomed out, and I felt as though time stood still.

"In these sorts of two-way interactions that we have with our children, they are very all-encompassing for us," says psychologist Ruth Ogden at Liverpool John Moores University in the U.K. "They are joyful moments — something that you treasure forever. And that means that when you're in them, you're not thinking about anything else."

So our brains are able to process a lot of information in those moments, making new memories. Even now, when I think back to that morning, I can clearly remember the tiny icy needles on individual leaves of grass, the tip of my son's index finger as the frost melted back into dew drops, and the awe in his eyes as he learned something new about the world around him.

But if parenting is full of these beautiful memory-making moments, why then, do our kids' childhoods seem to go by so quickly in retrospect?

That has to do with the less fun part of parenting, explains Ogden.

Mix up your routine

"Parenting is full of routine, it's full of organization. It's full of – for want of a better word — monotony."

Consider the routine of caring for a newborn. "You spend a lot of time in the house, you spend a lot of time trying to get them to go to sleep at the same time," she explains.

It's tedious, boring work that makes us parents operate in auto-pilot mode, because we've done it a hundred times before.

It's the type of work that doesn't make new memories, says Tse.

Even if we were to be attentive and present during every diaper change, he explains, our brains wouldn't file away a new memory for each diaper change, or every walk to the daycare, because it's not processing them as new events.

"In retrospect, they just seem to have either not happened or they get squished together with all the other similar events," he says. "So your sense of time retrospectively is compressed."

But there's a way to counter this, says Ogden, by focusing less on routines, and more on creating those "beautiful, incidental moments" with our children.

She herself has been trying to incorporate new and different activities with her kids.

"The more you break the day out with different activities or different things to do," she says, "then the more chance you've got of making these nice memories — the things that you're going to remember, the things that are going to help to stretch out your retrospective feelings on how the years passed."

As I think more about these past few years with our son, I realize that last year — 2022 — seemed to have lasted longer than the two years prior. And that's probably because we purposely broke away from some of our routines with him to have new experiences, and make new memories as a family.

We traveled more with him across the United States, as well as to India — our first time taking him to meet my family. My father, who lives in India, visited us for an extended period of time. So he could finally bond with this grandson and share in the joys of walking him to daycare and back. We went camping in Maryland over the summer — with my 79-year-old-father and our 2-year-old — an adventure we will remember for the rest of our lives.

And as I write down these precious memories, I also realize that it may be just as important to actively recall and share them with our son as he grows up and the years go by. Perhaps that's another way to slow down time — and remind us all that childhood doesn't happen in the blink of an eye.

This story is part of our periodic science series "Finding Time — a journey through the fourth dimension to learn what makes us tick."