Continuity mistake: Jack drops the two vials into the Tom Collins glass, while in the bathroom. At the hand-off, when he places the drink on the tray, there are no vials in the glass - there is no ice blocking them from view, just a skewer holding a maraschino cherry, a wedge of lemon, and a straw - no vials. Even Jack can't make the two vials invisible.
Continuity mistake: When Jack and Greg are in the motor home near the beginning of the movie, Jack is talking on the intercom mic to his family in the back, then puts it down when he is finished. But, in the following shot that shows Greg talking, you can see Jack's reflection on the window, showing him still talking into the mic.
Continuity mistake: When they all first arrive at Roz and Bernie's, Jack brings LJ over in the stroller. As Bernie babbles, "Bazooka, bazooka," and LJ starts crying, the stroller's orange flap (between LJ's legs) is attached to the front harness around the boy's waist. In the previous couple of close-ups of Little Jack, the orange flap hangs down between his legs.
Visible crew/equipment: When Pam and Greg walk to the RV and open its door, in the next shot just as Moses chases Jinxy, behind Jack, Roz and Dina, the reflection of a hunched over crew member, wearing a red shirt, is visible. Don't confuse his reflection with Bernie's, who is also wearing red.
Continuity mistake: When Greg does damage control in Roz's office by hiding things, the height of the table is about Greg's waist level - also note the wood paneling trim. In the previous shot, as Greg surveys the room, the table is a foot lower, which is also seen in other shots including when Greg enters the room, after the football game, to check on Jack and the table height is level with Greg's thighs. The entire table was deliberately raised in the close-up.
Visible crew/equipment: After Jack says, "Only the captain gets to make announcements, Greg," in the next shot of Greg the boom mic and pole are nicely visible over Jack's reflection in the window, to Greg's right. There are two other shots of Greg at this angle - one previous and one following, but unfortunately the equipment is not seen.
Continuity mistake: During the scene when Gaylord's dad has just found out that Pam is pregnant, Bernie enters the room with a bottle of champagne. he crosses to the bed whilst removing the wire top of the cork in preparation of removing the cork. Cut to Gaylord and then back to Bernie and he is removing the wire again.
Audio problem: At the end when Greg and Pam get married, Kevin plays a song on a set of pipes, however, the notes he plays are wrong - when he blows the short pipes, a low note is made, and vice versa. This should be the other way around.
Continuity mistake: When Jack places Jorge's hair in the test tube, he holds Greg's vial, and the name "Greg" is written with the first "G" beside the stopper. However, in the next shot, when he places the vials into the glass, the name is actually written the opposite way, with the last "G" beside the stopper (this is also seen earlier, when Jack inserts Greg's hair). Tape and handwriting differ as well.
Continuity mistake: As they are all outside drinking Tom Collins', the 2 cherries in Greg's drink are at the bottom, then when he leans in to answer Jack's question about his 'sister', the cherries are now at the top of his glass. The cherries actually switch back and forth in several shots.
Continuity mistake: The time frame doesn't make sense when the kid glues his hand to the glue bottle. He turns on Scarface, which is nearly over. The Fockers and the Byrnes are still in town shopping and Little Jack smears glue all over his hands. By the time they get home from town, the glue bottle is well stuck to the hands. However, Scarface is still on and still on the last fight scene.