When Sue Ellen is asking Kenny to turn the music down, she says "When are you going to start helping me, you lazy little punk?" If you look carefully she mouths the word "prick". As mentioned in the trivia section, director Stephen Herek decided he didn't want to take any chances of the movie receiving an R rating so he had the scene fixed for Sue Ellen to call Kenny a lazy little "punk" instead.
At the beginning of the movie, Kenny arrives home with a marijuana plant in a bag, which he puts on his window. The plant falls down and we hear a ceramic pot breaking, yet when Kenny was putting the plant down, we could clearly see the pot was plastic, not ceramic.
When Sue-Ellen has just come home from work, she puts her purse on the kitchen island. In the next scene at the office the secretary is going through Sue-Ellen's things and finds her purse and goes through it, finding her driver's license and discovering that she is only 17.
The film is set in the summer of 1990, but the Q.E.D. report on Sue Ellen's computer screen lists March 22 1989 as the day's date. Its confirmed it is meant to be 1990 by the posters in the Clown Dog advertising a circus for Friday the 20th of April (a date which falls in 1990, not 1989)
When Kenny goes to the window to see that Walter has fallen from the roof he clearly has to rips in the seat of his jeans, just below the pockets. Later at the hospital he only has one rip in his jeans, much lower on the left leg.
The gun Kenny was using to shoot the dishes was actually a bee bee gun. You can clearly see, but the sound and effect it was having on the dishes was a shotgun. Plus no shells were being ejected from the gun.
When Walter breaks his leg, Sue Ellen arrives at the hospital and he has already been treated. When she arrives she tells them that she is his mother. No paperwork whatsoever was involved. You cannot treat a child without a parent. When she arrived, he was ready to go.
Characters refer to Sue Ellen as being 17 years old. However, technically she is 16 as her birthday (as printed on her driver's license) is 19 December 1973. As the events take place during a 1990 Los Angeles school summer, it would not be December yet, making Sue Ellen 16.
Several times in this movie the children refer to themselves being on summer vacation. However, based on several points of the movie showing dates, it cannot be summer: the computer reads March 22, 1989 at the office; also the tickets Sue Ellen receives as a gift read April 1st, 1990.
When Sue Ellen is on her bed talking to Nicole on the phone, she is seen coloring purple stripes on a shirt in a fashion ad from a magazine. When the kids come in to complain about the babysitter the stripes are not yet colored in.