Revealing mistake: When Doug tells Arthur his toast is done, there is no smoke, but as soon as he is finished speaking there is smoke coming from the toaster. (00:04:05)
Revealing mistake: When Doug stops to tie his shoe outside the car dealership and Carrie walks up to grab him, you can see the fake back-drop sway with her motion. (00:08:35)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.