A Baby boomer is anyone born after World War II. In the United States, baby boomers are usually considered to be people born between the years 1946 and 1964, although some sources have different guidelines for what baby boomers really are. After World War II so many people started families that the birth rates went higher and higher. Nearly 72 million to 80 million babies were born in the United States during this time. During the late 1960s and early 1970s, the birth rate fell a lot.