Stepping Up: As the incarceration rate among mothers in the US increases, who cares for the children left behind?

A clean dusting of snow coats the hoods of cars parked along Philadelphia's West Norris Street. The trees are mostly bare, withered leaves buried in the corners of benches. This winter morning, the massive rust-brick complex, a low-rise housing development known as the James W. Johnson Homes, is serene. The complex, which stretches for blocks, comprises 522 apartments spread across fifty-nine buildings. The front doors form a confetti of colors—vivid yellow or faded blue, forest green or desert brown.

Shirley Johnson, seventy-eight, emerges from behind a crimson door, closing it and the steel security gate behind her.* Her white puffer coat is zipped up against the cold. The platform lift is broken again, so she inches down the stoop, gripping the iron handrail with both hands, until she is standing in front of her apartment, leaning on her walker. She appears even smaller than her true five feet. In a few minutes, the free shuttle arrives, and she's off to the senior center.

When she arrives, she settles in at a table with two of her sisters and several friends. Johnson sips her coffee and carefully pulls apart a cheese Danish; she'll spend the day exercising, having lunch, and talking smack about who's going to get a "head rub" or lose one of many intense games of pinochle. For a decade or so, this tribe and these meals have been her respite. She returns the favor by volunteering to call bingo on Wednesday nights.

On most evenings, Johnson makes it home by five to find her teenage granddaughter, Kayla Davis, watching TV or texting. Johnson will settle down on the couch, ask Kayla about school, though the girl will usually brush those questions aside to ask about the senior center, if Johnson made a new painting or sculpture, or if she happened to bring home a sampling of that night's dinner. Sometimes it's baked fish, sometimes chicken cheesesteak or shrimp fried rice. "I don't do all that cooking no more," Johnson says. "If she wants to eat, she cooks." Kayla can hold her own now in the kitchen, having served as her grandmother's sous-chef for years. She was only ten when she learned how to fry chicken without getting splattered by the oil, as Johnson, fighting arthritis, directed her from a chair. She now has her own rhythm in the kitchen.

On this winter night, Kayla sits in the kitchen dicing blocks of cheddar for macaroni and cheese. With each ingredient—milk, butter, eggs, seasoning—Kayla calls out to her grandmother for the exact measurements. Finally, she whips the mixture until it braids together. "I have to do it like you do it, Mommy, or else it ain't gonna taste right," Kayla says.

Johnson is Kayla's paternal grandmother, but she's been a live-in parent to Kayla since she was an infant. Johnson's son, Trevor, was serving a three-year prison sentence when Kayla was born; her mother, Ebony, was, according to Johnson, battling drug addiction and cycling in and out of jail. After a few years of raising Kayla informally, a judge granted Johnson permanent custody, at which point Kayla joined her sister, Shantelle, who, as a grade-schooler, had already been living with Johnson for several years. Over the years, Johnson has cared for four of her son's children for various stretches of time. Shantelle and Kayla are the last of the grandchildren living with her.

Johnson is one of thousands of grandmothers across the country raising a second generation of children while their parents sit behind bars, an unintended consequence of decades of mass incarceration. As of 2010—the most recent data available—an estimated 2.7 million children in the United States had an incarcerated parent. Studies show that when fathers are incarcerated, their children generally live with their mother, but when mothers are incarcerated, their children mainly live with grandparents and...