The task seemed easy enough.

At the beginning of the school year, my son’s kindergarten teacher requested that each student bring to class three items that weren’t on the regular school supplies list.

One was a spare outfit. If you have children, this needs no explanation. And if you don’t have children, then you have fortunately never opened a backpack to find a Ziplock bag stuffed with damp clothes.

The second item was a blanket for those students who still took naps. Or maybe it was slippers. Truthfully, I only remember that it was something within easy reach because I didn’t have to add it to any mental to-do list — unlike the third item.

That third item pestered me for days, and then weeks, tapping on my shoulder every once in a while to let me know it was still there, waiting. I eventually accepted that I was never going to get it done. I purposely pushed aside thoughts of it and convinced myself that his teacher had forgotten anyway.

She hadn’t.

A few weeks ago, halfway through the school year, I opened my dinosaur-obsessed kid’s dinosaur-themed backpack, and there it was — a gentle, but undeniable tap.

A slip of paper let me know that he still hadn’t brought in a framed family photo.

We live in an age of smartphones and tablets and doorbells that are capable of capturing acts of thievery and kindness. Cameras are all around us all the time. Finding a family photo should have taken a few minutes. It should have required a quick scroll, click and print.

It should not have been a source of stress.

And yet, there I was, stressing because I couldn’t think of a single current family photo to send.

I have a phone and iPad filled with images of my two sons. I have pictures of them together. Pictures of them with their dad. Pictures of them with their grandparents. I even have a picture of them with the neighbors.

I was there for all those photos. But I’m not in most of them for reasons that other moms can probably relate to: I was either taking them or trying to stay out of them.

If you look at photographs of babies and toddlers taken in the 19th century, you will notice that some of those children are propped against strangely shaped, cloth-covered lumps. Those lumps are actually their mothers.

The long exposure times that cameras required meant photographers had to get creative and mothers had to get lost — sort of. They became props and backdrops. Mothers, and motherly stand-ins such as nannies, were tasked with both keeping the children still and staying out of sight.

Those images eventually became know as “hidden mother” photos, and they are fascinating and unsettling. In some, the women resemble ghostlike figures looming behind babies. In others, their faces appear painted over or scratched out.

“These photographs range from the comic, almost slapstick, barring of the mother to more macabre examples of her literal erasure,” is how the Palmer Museum of Art at Penn State described them when it held an exhibition on those photographs several years back. “Never meant to be seen, her presence nonetheless haunts these images.”

A lot has changed since draping sheets over moms seemed normal. And yet, too often moms still don’t appear in many photos of their children.

The proof can be found on parenting sites, in personal essays and at playdates.

Once at an outdoor birthday party, my younger son climbed into my lap to recharge for a few minutes before darting off again. As he rested his sweaty head against me, another mom raised her phone to take a photograph. Before I could tell her not to bother, which is what I tended to do even before I had kids, she said, “No one ever takes pictures of moms.”

That’s true. Mom moments have a way of blending into the background in a way that moments with other family members don’t. Grandma reads a book to the baby and we know instantly we want to preserve that image forever. We read to that child every night for years and it doesn’t occur to us to capture it even once.

Sure, plenty of moms take selfies with their children. I have plenty of those. But those images aren’t what children will later scrutinize for clues about their childhood. For that, they will turn to candid photos, those images snapped in unplanned moments when you don’t have time to even brush that hair out of your face. Those are the photos that are both tempting to avoid and yet are the important ones because they go beyond how moms look and capture how they live, how they mother.

The hard part is trying not to duck out of them. Trust me, I get it. So many of those moments when we are mothering our best we don’t look our best. Our hair is unruly. Our faces are bare. Our bodies are braless. In some of the photos and videos my husband has taken of our children and me, I am holding up a hand to wave the camera away.

I never thought much about those moments until I had to sift through thousands of our images, looking for that family photo to send to my son’s class.

Only then did it hit me that even though I’m a main character in my kids’ lives, I appear as a guest star in our photos. In that way, I am not so different from those “hidden mothers” who were both present and absent.

I don’t know if I will have decades or years or less to form memories with my children, but based on the photos that exist now, they wouldn’t fathom a fraction of the ways I try to show them how much they matter to me. They wouldn’t see me standing in my bathrobe at 7 a.m. mixing pancake batter with food coloring to make a red T-Rex for one of them and a blue shark for the other because those are their favorite creatures. They wouldn’t see me wearing a cheap superhero mask chasing pretend supervillains alongside them. They wouldn’t see the bags I get under my eyes every time they get sick because even when they sleep, I’m still up worrying.

While going through our pictures, I made a quiet promise to myself. I would stop waving away cameras no matter how I felt I looked, I would try to be more like that mom at the birthday party who had already figured out what it would take me a few years to learn, and I would make more of an effort to get at least one quality family picture a year.

The first and only time we took professional family photos, we were living overseas and I couldn’t resist the natural backdrop and affordable photographer fees. I treasure those images. I also knew there was no way I could send one of them to my son’s class.

In them, he is 1.

Then I remembered one other family photo. It was taken at one of those photo-booth-like setups at my niece’s wedding in Texas. In it, my older son wears a gray suit and a matching cowboy hat, and my younger son, who was the ring bearer, sports a black tux.

He was 3 at the time, and I wondered if it was too dated for him to take to his class. But then I saw him look at it — at us — and light up. He asked me to send it.

I printed it, framed it and tucked it in his backpack.

I also emailed his teacher to apologize for the delay and explain why a simple task had taken me so long.

She replied with an assurance that she knew how hard it could be to find a good “or any” family photo.

Of course, she understood. She’s also a mom.

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