Continuity mistake: In the drugstore scene, young George is holding up his latest issue of National Geographic magazine for Mary to see, but the next shot shows George bending down to fill Mary's ice cream dish.
Audio problem: When George and Mary are walking up to the dilapidated house (prior to throwing rocks at it), George is talking. At one point he is saying something and his lips aren't matching.
Continuity mistake: At the beginning in the soda shop, the first little girl (Mary) is facing toward the camera, away from the other girl that comes in. When they start talking however in the next shot, both are facing outward.
Answer: It was a common phrase at the time, like someone saying "oh boy!" or "hot damn."