Continuity mistake: In the opening shot at the breakfast table, there is a large cereal box and a carton of milk on the right side of the table, in front of two salt-n-pepper shakers. But during the scene it continues to swap to an angle behind the two shakers - but now the cereal box and milk carton have vanished, so as not to block the view for this angled shot.
Continuity mistake: When Sharkboy and Lavagirl burst into the classroom looking for Max, there is writing on the blackboard ("Science, Chapter Two") written in yellow chalk. Strangely, later in the scene the writing is now written in white chalk, and the handwriting of the text is noticeably different. Then, later it goes back to yellow!