Plot hole: When Charlotte kissed Naveen at the end, she should've turned into a frog as well because she was no longer a princess.
Suggested correction: When ordinary people kiss a frog, they don't transform into anything. (Perhaps they die from infection after a few days.) Charlotte was just an ordinary person. Tiana was chosen. She wished upon the star. Naveen and the consequences of kissing Naveen were a result of Tiana's wish.
Suggested correction: How? She was no longer a princess.
Tiana turned into a frog because she kissed Naveen without being a princess, so Charlotte should have, too.
Plot hole: In the scene where Ricky is fighting granny, she elbows Ricky in the neck and knocks off the alien control sensor. But later when he goes to the other girl's house, he is once again controlled by the alien joypad (without a sensor on his neck). (01:02:15 - 01:19:40)
Plot hole: At the concert in Crowley Corners, Miley announces that she will sing a new song she just wrote, "The Climb." Somehow the band and the backup singers all know the words and the music.
Plot hole: There is no possible way for the chubby mayor to be able to get in Flint's lab. There is no side entry, and the space other characters use to get in is too tight for him.
Plot hole: In the first film, the shape of the ring was a little different and it was set in a ring. Also, it was given to Xania. In the second film, she was never even acknowledged as donating it to the museum.
Plot hole: Mr. Cranston asks Denise to be the accompanist for the school's production of "Chicago". This is an error. In the year 2009, in which the film is set, this would be impossible since the licensing company which has the theatrical rights for "Chicago" restricts the show from being produced (even by amateur groups and schools) anywhere in the greater New York area while there is an open-ended production running on Broadway.
Plot hole: In the series we learn that these creatures take a lot longer than us humans to grow up and that they live a lot longer. They mention that the children are about 900 years old, so a grown-up would be more than 1000 (probably 2000). The series is set around our time (1990s/2000s) and Fjellrose and Erke are very old. Yet the film is set about 100 or 200 years ago, you can tell by the way the humans are dressed and the way their houses are built etc. So Fjellrose and Erke should still be grown up, but they are young children. If they are only 100 to 200 years younger, then they should be much older in the film or much younger in the series.