When the girls spot the nerds, Kimmy stops the car behind the stop line. When the nerds walk in front of the car, the front end is hanging over the line without having been moved. When the girls get out of the car, it is behind the line again.
When Jesse takes the pentagon-shaped block, the twin in the red shirt is opening his cube with his left hand. In the next shot the cube is closed and the twin's right hand is resting on top of it.
Jesse leaps to get the admissions letter out of the garbage and knocks the table lamp over. In the next shot, the table lamp has been picked up and placed back where it belongs.
When Nicky and Alex play with the blocks on the lawn, at one point a small chunk of the lawn sinks then pops back up, indicating it is actually solid pieces of fake grass.
Nicky and Alex get accepted into pre-school. They finally show up two years later.