Continuity mistake: At the very end of the movie the 3 girls are performing on stage. Agnes is wearing white tights, but after the platform raises them all above the house she no longer has tights, just bare legs.
Continuity mistake: In the scene where they're in the air close to the end of the movie, when Margo tries to jump to Gru's plane, Vector grabs her and points the squid launcher at Gru, then the moon hits Vector, knocking him and Margo off his ship. When Vector climbs back up to his ship, the moon's gone. It couldn't have rolled away because Vector's ship didn't move in that short time.
Continuity mistake: In the very first shot of inside the orphanage, the tape mark on the floor is at least 3 feet away from the desk. The three girls stand behind it and 2 shots later we can see they are standing about an inch away from the desk. Then when Miss Hattie stands up, the tape is now a foot away from the table.
Continuity mistake: Justin, the boy with the toy aircraft running away from his mother, towards the pyramid in the beginning of the movie, has the toy in his left hand while going up the ramp, while falling and as he begins traveling up through the air but when the angle of view changes it is in his right hand until he lands on his father. (00:02:05 - 00:02:45)
Continuity mistake: After Gru tells the first minion "Minions assemble", that minion slides down a pole and relays the instructions to other minions. After he does this you can see a minion standing on the right of a blue tube and he jumps in, after the camera begins to pan to the left, that same minion instantly appears back at the entrance of the tube. Probably an error in the animation sequence which returned the minion to his starting position when his animation was finished.
Continuity mistake: When Gru is explaining his plan to the minions, one of them takes out a torpedo and fires. The torpedo is held by one of the taller minions at first, but after the torpedo has fired and Gru says "Hey, Dave", we can see the torpedo was held by one of the smaller minions.