“Here, then, are cases in which the fear that violent pedophiles might abduct children from public places—a vanishingly rare occurrence—was used to justify the punishment of women who were looking for work, women who were at work, or women who simply thought that she and her child might both benefit from the child being allowed some time to play on his own—in other words, women whose failure to devote every moment to their role as mothers was viewed as literally criminal.”