Multi generations in a house was certainly a thing though it varies depending on what decade you're talking about. The houses definitely were smaller as were the yards. Look at the new construction now, there are no modest sized homes being built then drive through an older neighborhood. There is simply no comparison. My aunts and uncles all shared bedrooms.. Rarely did houses have more than one bathroom. Nobody had central air conditioning not homes, not schools. Plenty of teenagers have cars these days though they're still in school. Nobody walks or rides bikes unless they're electric. Most people are overweight and plenty of young folks are diabetic. Those factory jobs that everyone thinks were so great? They were often dangerous before OSHA and unhealthy before the EPA. My older neighbors in Cleveland told me about the soot from the nearby steel mills. BTW those jobs were plentiful until recently where I live. They're miserable places to work still. They'll make you work 6-7 days a week, 10-12 hours a day. My sister just got fired from one making $25 an hour, she lost a similar job year ago. Everyone is doing Adderall to cope, management looks the other way.

Drive through older neighborhoods and look for yourself. Also you can look up real estate property info on most county websites in the US. They'll tell you square feet and also the year built. Builders these days don't build reasonably sized homes unfortunately. I wonder if cities don't want them because it'll attract lower income folks. As for multi generations in the same home, I recently had a subscription to Ancestry.com and could see all the people living in one house as was recorded in the census data. Families had more kids too.

A lot of those rural homes had an addition with each generation. Most families lived in 1200sq ft or less. The average size of a home has risen pretty dramatically.