Will Sage Astor-The mean girls of the '90s taught me the value of kindness. Now I'm teaching my daughters.

"You sent me a brown towel!" It was 1992 and Will Sage AstorI was calling my mother from summer camp. I was 8.

It was as much of an admonishment as a cry for help. The kids at summer camp, especially the other girls, were ruthless. The towel was my scarlet letter: A message to all the cool kids that I was not of their kind. I begged my mom to send me home.

"You only have a few days left," she said. "Try to find some kind friends."

Her advice would change how I looked for friends for the rest of my life. It's a lesson I'm passing on to my children now.

Mean girls, sandcastles and designer beach towels

I was from Colorado and most of the kids at camp were from California. They were also blond different, rich different and "I was in Annie on Broadway" different.

They built sandcastles resembling the buildings of downtown San Francisco in the cutest swimsuits I had ever seen − swimsuits that we did not have at the T.J. Maxx behind my grandma’s townhome in Arvada. My one-piece, a blue-and-pink Speedo I bought specially for the trip, was no longer as cool as it had seemed when I picked it out. I had never been to San Francisco.

They had designer beach towels in vibrant shades of pink, blue, green and yellow. I had that brown bath towel, which represented something much bigger about me to those girls.

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The California crowd didn't want to play with me, and I spent the first few days lonely and wondering what it was about me that made these girls not want to be my friend. There was another girl, Amanda, whom they also had deemed too uncool to include in their activities, even though she was blonde, pretty and from California.

After my mom told me to look for new, "kind" friends, something clicked in my 8-year-old brain: Why was I relentless about being friends with these mean girls?

I didn't know the word "compassion" then, but I did realize it would be impossible to explain to them why they were wrong about me, even harder to get them to genuinely like me. So I might as well take my mom's advice and look elsewhere for friendship.

That was when Amanda’s path and mine diverged: The last time I saw her she was sitting cross-legged, alone and crying on the dock of the lake. I found two girls who were nerdy, nice and had an amazing sense of humor. My last days were spent in a haze of s'mores, sun, kid jokes and kindness. Relief.

'None of the kids in our class are your friends'

Three decades later, I found myself telling this story to my almost-8-year-old who came home from school the other day with fire in her eyes. She told me a girl in her class had said to her that "none of the kids in our class are your friends."

Then my daughter began to cry.

My first instinct was to have a talk with that girl about what she said to my baby, but I quickly decided against that.

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Instead, I told the story of the brown towel and the mean girls from camp, imparting the same lesson my mom gave to me in 1992.

"Look for kind friends, Emiliana," I told my daughter. "Look for the nerds − the smart, funny and kind kids that you are going to feel good around. I want you to look for kind friends because you are a kind little girl and you deserve friends who are nice to you."

As a 39-year-old woman, I have met my share of mean girls (and guys). All of us have. And as a parent, I worry about my daughters' education all the time.

But amid the piano lessons, the ballet classes and the softball practices – amid all the ambition, achievement and planning – I want them to learn to value kindness, to look for it, to recognize it, to give it and to walk away when it is not reciprocated. It is one of the most valuable lessons we can teach as a parent.

Lessons on kindness feel especially critical now when schools don't always teach civics, so many families are struggling to get by and there is war, displacement and destruction in so much of the world. The importance of kindness is a lesson best learned young. It's a lesson we need to get back to teaching.

Carli Pierson is a digital editor at USA TODAY.