The Little Pink Book/Field Trip - S1-E2
Other mistake: Field Trip: When Lockjaw goes back into the water after Harold throws his ice cream at him, there is a shot of Arnold looking sadly in Lockjaw's direction, and he is behind the wall like he should be. Two shots later, he is mistakenly placed in front of the wall instead of behind it. (00:15:28)
The Little Pink Book/Field Trip - S1-E2
Other mistake: Field Trip: When Grandma uses the grappling hook to climb the wall, she falls to the other side, and she clips through the grappling hook. (00:19:17)
The Little Pink Book/Field Trip - S1-E2
Other mistake: Field Trip: When Arnold is telling Grandma about Lockjaw, right before Grandma gets up from the couch, her left foot is meant to be on the floor, but it is instead overlapping the couch. Then, when she marches up to the couch while saying, "Like he's some sort of common criminal," her right foot overlaps the couch, and Arnold is kneeling on the backrest of the couch instead of the seat as he should be. (00:18:01)
The Little Pink Book/Field Trip - S1-E2
Continuity mistake: On the "Presidents of the United States" sign behind Helga, the word "United" becomes "Nvited"
The Little Pink Book/Field Trip - S1-E2
Continuity mistake: Arnold is talking to his Grandma about the turtle. There is a table in front of them with three items on it: a remote, a magazine, and what looks like food with a cup. In one shot, the items move around at least twice, depending on which angle the shot is.
The Little Pink Book/Field Trip - S1-E2
Continuity mistake: The orange juice container on the table jumps around when Arnold's grandpa is talking to him about his crush. First it's in the middle of the table, then it moves right. Then back and right again.
The Little Pink Book/Field Trip - S1-E2
Continuity mistake: Arnold puts the pink book on top of a bookshelf at an angle. When Helga comes into his room moments later, the book is upright.
The Little Pink Book/Field Trip - S1-E2
Other mistake: When Arnold is reading the diary at the school the other kids ask him to read more. He says "OK, but it is the last page." There are more pages. When he starts to read, then it is the last page.
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.