Continuity mistake: In the very beginning the camera is panning, showing Ralph's house next to an empty lot and continues past, showing that across the street is a corner house with hedges. So Ralph's front window would be staring up a street and a line of hedges running up the street. When his father wins the award, the neighbors have their backs to the hedges with the large white house in back of them. This would have them staring across the other street, not at Ralph's house.
Factual error: Early in the film, while the kids are looking at the toys in the Higbee's store window, two uniformed soldiers are visible right behind the kids. The female soldier is wearing sergeant stripes on her sleeves, but the braid on her garrison cap is gold - a color reserved for commissioned officers.
Factual error: In the beginning of the movie, when they are in front of Higbees, there is an RTA sign on the building in the background. RTA in Cleveland did not exist until around 1975.
Other mistake: When the old man screws in the blue light bulb on the Christmas tree and the lights go out in the house, the living room remains dark while he changes the fuse. Meanwhile a fire is going in the fireplace, so the light from the fire would cast some light into the room.
Audio problem: During the Santa scenes, Ralphie and his brother are lying in the fluff at the bottom of the slide. You can still hear kids screaming because of Santa. Nobody else is sent down the slide at that point and the camera pans up to see Santa with a calm little girl on his lap. Where are the screams coming from?
Revealing mistake: When they close up on the boys at the flagpole you can see what is probably a pole support bar going down at 45° from the flag pole. Though looking too straight for flexible tubing, this could alternatively be an air suction tube that was used in holding Flick's tongue to the pole.
Continuity mistake: First breakfast scene, the stack of toast moves from Randy's end of the table to Mom's end.
Audio problem: When Ralph and Randy are in line waiting for Santa, if you listen closely Santa keeps repeating the same lines like "And what do you want for Christmas, Billy?" "get him off my lap," "Santa can't wait all night let's go!" "HO HO HO!" but in the exact same tone, the child and Randy's screaming is also on repeat too.
Factual error: In the opening street scene a Salvation Army band is playing Christmas carols. These arrangements were not written or published until the 1950's.
Continuity mistake: When Ralphie and Randy go to see Santa (after the parade), their parents leave them alone to wait in line. Listen carefully to Santa in the background. You can hear him mention a boy who's wet and saying to get him off his lap as Ralphie and Randy go to wait in line. This is the same boy who we don't see until Ralphie and Randy are on the stairs leading up to Santa.