In the early days of the COVID-19 pandemic, a photo of two little girls in the parking lot of a California Taco Bell went viral. They were doing their schoolwork on laptops in that inconvenient location because the restaurant provided free Wi-Fi, which they didn’t have at home. The girls came to symbolize the digital underclass that’s emerged since the rise of the internet. There are millions of American kids like them, says Nicol Turner Lee, senior fellow at the Brookings Institution. Her analysis of the digital divide is contained in her new book, “Digitally Invisible: How the Internet Is Creating the New Underclass.”