When David is sitting next to Meg on the bed while the police officer is questioning him, he has blood dripping down the left corner of his mouth from being beaten. When they show a close-up, the blood is gone and the dirt but when the camera switches back to the side view, it's back again.
When David is talking to his father about when it's okay to hit a girl, his father sets three bottles of alcohol out on the bar. There's a close-up as David stands at the bar and, when the camera pans out, the three bottles are gone without David having moved to put them away.
In the last scene, there is a close-up of adult David kneeling by the water with a duck paddling in the background. When it turns into a long shot, the duck is gone.
As Meg dies, David's right hand is holding hers in between the two of them. When the film cuts to the next shot, his right arm is draped around her.
In the scene at the park where Meg is seen talking to Officer Jennings, on his police car it clearly is labeled "Highway Patrol". It is not a Highway Patrol officer's job to preside over such events, nor is it to investigate possible child abuse situations.
When David goes to talk to his Father at work. There are several Liquor Bottles sitting on the Bar that had UPC symbols on them. UPC symbols didn't come out until the late 70's or very early 80's. The story takes place in 1958 way before UPC symbols existed.
The American flag hanging on David's front porch is the 50 star version that is currently in use. However there were 48 states at the time the movie took place (1958), thus only 48 stars on the American flag.
Though set in 1958, kids call one another "dork" and "doofus" - gradeschool put-downs that weren't in common use until Seventies or Eighties.
In the basement when Meg is tied up and undressed by the boys on the order of Gertrude. The underwear she is seen wearing while appropriate for her age group (12-16) as she is 16, they would not have been manufactured until around the time of the films production and release.
David's hair is of a length that would have had him tormented. 50s men's and boys styles would be greased (Brylcream) but never long in back. The Mullet was decades in the future. David,s hair is longer than when the Beatles first appeared.
The first time David goes down stairs he's wading through hanging laundry. When he goes through the last sets of linen another hand can be seen on the left helping him pull the laundry aside and hold it there, presumably, for the camera.