EVERY MORNING , my young daughter and I walk from our apartment just above ground zero in Lower Manhattan to her school in the shadow of the Brooklyn Bridge. We cut across Federal Plaza and pass the line forming between policed barricades designated U.S. IMMIGRATION AND NATURALIZATION SERVICE, as the early light illuminates the inscription on the courthouse frieze: THE TRUE ADMINISTRATION OF JUSTICE IS THE FIRMEST PILLAR OF GOOD GOVERNMENT.

On one of these bright autumn mornings Beatrice discovers the pill bugs that climb out of the shrub beds and make their way across the plaza. She delights in the way they tuck up their tiny legs and curl into armored balls when poked. I am pleased with her affection as I worry that raising children in the city will distance them from the charms of nature.

Once these little creatures come into her focus, their perilous plight to cross the plaza becomes her own. She crouches down plucking up one after the other, carrying them to safety. Most children have an innate sense of compassion, and in Beatrice, this mixes with a fierce determination to forge the heart of a small superhero. After she rescues one pill bug, her six-year-old moral convictions make it impossible to leave the others behind. But school awaits, and I tug her along, whimpering.

Back home, we research pill bugs. Beatrice wants to know why they would make such a foolhardy trip. “Maybe they put poison in the dirt,” she says, remembering the signs we saw warning of rat poison, “or they needed to find more food.”

Google does not tell us why the pill bugs are on the move, but it does deepen our love for these tiny travelers. We learn they are not insects or arachnids, but rather crustaceans. Their distant cousins are lobster and shrimp; their ancestral home, the sea. In fact, pill bugs and their kin are the only known crustaceans able to live their whole lives outside of the water, though they do require a moist environment to survive. Their iconic ability to curl up into a tight ball distinguishes them from their close relative, the sow bug, and gives them the lovable nickname roly-poly.

We are incredulous that most resources focus on how to exterminate these intrepid creatures, how they are commonly considered pests. Harmless to humans and pets, pill bugs don’t bite or carry diseases, or damage houses or clothing. They may snack on garden seedlings, but mostly they recycle decaying matter and contribute to soil health.

By the time we finish our research, Beatrice has hatched a campaign to save the pill bugs of Federal Plaza. Using markers and poster board, she draws a railroad-style gate that will lower to stop human traffic and allow the pill bugs to safely cross. Her earnestness makes my heart ache. I’m not ready for her to learn that such plans are impossible, that bugs will always be crushed under indifferent shoes.

The next morning is brilliant and crisp, and the marble plaza glows. Beatrice darts around, frantically airlifting pill bugs, her wild curls bouncing, her backpack bumping her bottom. I watch my child so at ease in this space, her own backyard. She doesn’t notice the guards with guns strapped on like messenger bags.

Most of the people we see gather between the barricades. Today I see a young boy with his arms wrapped around a leg draped in the long black cloth of his mother’s chador. The boy wears a stiff white shirt and dress slacks, the grooves of a comb still etched into his glossy black hair. I wonder how early his mother has risen to get here, how far she has traveled this morning and in days and weeks and years past.

I try to wait out Beatrice, hoping she will give up or move on to another passion, but she is committed. “Mommy, you have to promise to at least ask. Write a letter to the mayor and ask him. Use your voice!”

Beatrice and I often discuss our role in democracy. “We speak up, we get involved!” I preach. We made signs and marched with thousands of women in pink hats. We marched again with rainbow flags, then again with buttons declaring that students ought to be armed with books, not guns. We talk about skin color and fairness, about kindness, and how there is a time for anger, too. But I am weary, overwhelmed by the steady assault of devastating news. My entreaty to my daughter that every small act has the power to change the world often feels feeble and hackneyed.

That evening, I tell Beatrice her plan is a good one, but that the mayor cannot allow it. I explain that her desire to help the pill bugs is important: it means that she notices and cares about others. I tell her that she has a responsibility to this world, that her heart is big enough to love all its unique inhabitants, and that her mind is smart enough to come up with ideas that will help them.

“That’s okay, Mommy,” she says, “I already thought of another plan.” She tells me how we will paper the areas outside the plaza with flyers and get other people to help relocate the pill bugs. “We’ll save as many as we can.” O