Plot hole: When the Gales' house lands in Munchkinland, Dorothy picks up Toto and glances around the house. She looks right out the window. Wouldn't she have noticed that she wasn't in Kansas then, before she got to the door? (00:19:05)
Plot hole: At the end of the movie, when Rhett famously leaves Scarlett, she thinks about how she can win him back, and with a smile on her face, says, "After all, tomorrow is another day." Her daughter tragically died a few days before. Scarlett isn't the least bit heartbroken about losing her.
Suggested correction: This is not even a mistake, much less a plot hole. A character not acting the way an audience member expects them to is not a mistake.
It should also be noted that in the 1860s there was nothing unusual about a child dying. In those days, roughly 30% of children in white, well-off families like the O'Haras would die before the age of 5.