The gender of the dog Reckless seemed to change back and forth throughout the first several episodes.
Throughout the series the Waltons' Tardis-like garden shed appears to be much bigger on the inside than on the outside.
In a number of her scenes, Merie Earle, who played Maude Gormley, can be seen mouthing lines while other actors are speaking.
Traffic noises from surrounding streets and highways are heard in several episodes (exterior scenes were shot at the Warner Bros. Ranch in Burbank).
Olivia and John have light-blue eyes, as do Olivia's aunt and uncle and both of John's parents; but three of their children have dark-brown eyes. This is genetically possible, and excusable for artistic license, but it's almost unheard-of in the human population.
The show's prop department seemed to have issues spelling "forward" on recreations of Depression-era NRA posters. In The Deed (1973) it's misspelled as "foreword" and in The Bequest (1973) it's misspelled as "foreward."
In later seasons of the show, 1970s-era feathered hairstyles and long sideburns are sported by several characters, despite being set in the mid-1940s.
Although the family got a phone during later episodes, they still got phone messages through storekeeper/ manager Ike Godsey.
It's implausible that the Waltons, living in rural Virginia in the early 1930s, would have had electricity, gas and indoor toilets. The Rural Electrification Act was not enacted until 1936, and gas water heaters and indoor bathrooms would have been an impossible luxury. Water would have been heated on the stove and the family would have used outhouses.
The children are separated in school by age or at least age group (John-Boy and Jason appear to be in the same class) but in different episodes of season 1, Miss Hunter appears to the the teacher for John Boy and Jason, Ben, and Elizabeth.