Character mistake: While pitching his shrinking machine to NASA Szalinski claims that reducing the size of a rocket's payload would result in "staggering" savings in the fuel required at takeoff. However, he makes it clear that his machine works by reducing the space between atoms, meaning that the shrunken object weighs the same as the original. Weight is the critical factor in calculating fuel consumption, not size. Anyone at NASA would pick up on that instantly.
Other mistake: When Amy hits the button to tell her dad that breakfast is ready, he tries to type "I'll be down in five minutes." However, the message on the strip of paper says "I'll be down in five mimmicks." Amy says, "Typing with his gloves on again." Even if someone was typing with their gloves on, the blatant misspelling would not happen.
Visible crew/equipment: Before the neighbors enter the house and get shrunk, all the film crew and a boom mic are reflected on Nick's glasses.
Answer: More along the lines of a serious health problem related to her "plumbing".
Greg Dwyer