Continuity mistake: In the first film, George refers to the tree that the family carved their names in as being in the front yard. In the second film, this same tree is referred to as being in the backyard.
Continuity mistake: In the first movie, the wedding took place on January 6th. But in the opening sequence here the framed wedding invitation says "October 9".
Other mistake: In the scene where it's talking about the hottest summer the city's ever had (or something to that effect) some neighborhood kids are frying an egg on the sidewalk. The problem is, they're sitting and kneeling on that same sidewalk with their bare legs, and don't seem to be in any pain or discomfort.
Revealing mistake: The panicked drive to the hospital ostensibly takes place during the early evening, yet there is absolutely no traffic in downtown Los Angeles.
Continuity mistake: In the first movie Annie had lived in the house since she was five, something significant enough that they wouldn't forget. In the second movie, George and Annie had played their first basketball game at the house when she was four.
Revealing mistake: The monitors in the hospital attached to Mr. Banks's wife and daughter didn't move, although they should have shown something important about the patients.
Continuity mistake: Franc gives George two Vatsnik and he takes them both at the dinner table. George asks Matty to pass the rolls. Matty passes them with his right hand. When the scene zooms out and Franc, Nina, and Annie come into the dining room, Matty's left hand is on the roll basket.
Visible crew/equipment: When George and Annie are outside discussing the sale of the house and shooting basketballs, look out for the dolly track as the camera pulls back.
Other mistake: When George is holding his newborn baby and his grandchild, you can see that the babies are actually dolls and not actual babies. I guess it made it easier for him to hold in some shots.
Continuity mistake: In George's montage of memories, the girl playing Annie as a little girl looks completely different from the one playing little girl Annie in the original movie.