"The Children's Era" is an ironic title, because Margaret Sanger is saying that we're not in the Children's Era. (Other unused titles may have included "The Calorie-Free Pizza Era" "The Cats Are As Nice As Dogs Era" and "Free Penthouses For Everyone Era.")

The Children's Era doesn't exist—yet. By using this as her title, Sanger emphasizes the way children's welfare is neglected in the real world.

Sanger understands a point that often gets ignored by all sides in arguments about birth control. The child's welfare is directly related to the mother's welfare because the child will be affected by the mother's body during the pregnancy…and by literally everything else about the mother (income, physical and mental health, ability to parent) after birth.

Opponents of birth control have frequently characterized the use of birth control as an inherently selfish act, saying that people just want to have sex without consequences, and presenting the hypothetical children whose conception is prevented as victims. Sanger says nuh-uh: birth control is good for children. Birth control ensures that parents have enough time, money, and maturity to care for the children they do have.

Sanger knew that people didn't care enough about women's health and reproductive rights to get on board with her just for women's sake. Children, on the other hand—well, what jerk is going to say we shouldn't do what's good for the kiddos?

Certainly nobody in her audience, which is full of social reformers who like to think of themselves as leading us all to a better place called "the future."