Back Lots and Back-up Plans
My sister has been a member of the DGA for many years. She has worked on some movies most here would remember, but a lot were losers or intended to go straight to video, or nowadays DVD.
One of the lesser known films, Jack the Bear, was set in Oakland, CA and there was a need to create a working class neighborhood street. I presume the perfect scenes on the various studio back lots wouldn't work for this, so instead an entire street with facades of homes was constructed, complete with weedy yards, unswept gutters, junk cars etc. on the soccer field of a private school just east of Hollywood. I went to work with her one day and was amazed at how real it all looked, even in person. Her dobie mix Willie even got some fleeting camera time being walked down the sidewalk in one scene.
Regarding the Ozzie's Girls references made above, there were changes to other programs as kids grew older. The Donna Reed Show created a young girl's role, some sort of orphan who just showed up one day, as characters Jeff and Mary grew too old to get into the right kind of trouble anymore. I think My Three Sons also brought in a young boy at some point, possibly through the adoption of one of the son's friends, but I could be getting that show confused with another. MTS also had some poor acting from Mike's wife, as I recall.