Back in the 1960s there were four ways to avoid the Draft and getting sent to Viet Nam. Most people know about the first three which were (1) to mainatain Student status as long as possible (2) by pulling a "Slick Willie" and running off to hide in Canada and by (3) Pulling a "George W" and joining the National Guard. Back in those days the Nationa Guard was NOT getting called up en mass. Although Guardsmen still went through the same initial training just like active service troops, once training was over, they waved good-bye to their former buddies who got sent to Viet Nam while they just went back home to the states where they lived. The 4th way was by getting married and having kids. They still had to register for the Draft, but by havig a family, their Draft Number was so low it would have to take a foreign army invading US soil before they would ever have to go. In order for this to work, the family had to help that young man to get a job to support that young family. In ths movie, THAT was exactly what happened. The Dad sacrificed some of his paycheck so that a job could be created for his son, so hat the on could support his new wife, avoid getting drafted and avoid going to Viet Nam. This strategy actually took place within a large number of middle class American failies, but hs seldom been depicted by Hollywood.
