We just went to visit a family member who has a new baby. Oh, the sweetness! Being a few years removed from the newborn phase, I had forgotten how little they really are.

Of course, being on the onlooker side rather than the caregiver side is much easier. We all remember when our babies were newborns, but somehow it’s hard to appreciate it when you are sore, sleep-deprived and overcome by hormones.

As my sons (who look enormous in comparison) held this little one, I couldn’t help but think of that phrase we hear all the time, “Why can’t they stay little forever?”

What is it about our children’s inevitable growth that sparks these bittersweet feelings?

Some of it of course has to do with the innate appeal of all things innocent and small. We are all attracted to babies. Even my rough-and-tumble 4-year-old was enamored by the smallness of a newborn. It’s human nature to want to watch and protect another being so tiny and new.

So it seems the bittersweet part comes in as we realize that this innocence does not last forever. The one thing I’ve noticed with my 8-year-old is not so much my sadness at his physical growth, but the slow loss of some innocence.

We try to shelter and protect, but the outside world creeps in. That loss of innocence when they learn that first “bad” word from friends at school. That realization one day that they no longer want to watch Sesame Street, but rather superheroes that have some aspect of good vs. evil. We wonder why can’t the world just all be “good” and no “evil.”

Growing up, I remember my mom always saying she wished she had one version of each of us that stayed little and one that grew up. That’s a mother’s heart—we revel in their learning new skills, but mourn their growth at the same time.

At my stage in life, I sort of feel like I have that situation, even if for a brief time. With the youngest at 4 and the oldest at 8, they are like the past and the future versions of boyhood right in front of my eyes. To me the 4-year-old is still little. He still likes to be held and will cuddle. The 8-year-old is still cuddly, but is definitely not little. His gangly arms and legs hang off of me. But his maturity is at the same time refreshing and alarming. How can this boy that was just a rambunctious toddler be discussing everything from religion to math to space travel?

Yet at each new stage, there are new challenges. It’s no longer nursing and sleepless nights, but it’s now teaching them how to manage friendships and outside influences.

How to help them learn new freedoms and remain safe. With each stage we as mothers have to stretch further, face our fears and sometimes even relive our own childhood.

Maybe this is why we cringe at the passing of time and their growing maturity—because it forces us to grow, too.

Just when we think we have our kids figured out, they change. With each passing year, they are the catalyst for our development—for new experiences, for being more patient than we thought we could, for figuring out how to love this unique person.

Why can’t they stay little forever?

Because if it weren’t fleeting, then maybe we wouldn’t cherish childhood so much.

Because if we didn’t see them grow and flourish into maturity, then how would we ever see the fruit of our labor?

Because through their development, we push ourselves to be braver and love deeper.