Complex sentence: The Griffin family decide to travel to the Six Flags amusement park, but when Peter is barred from riding "The League of Extraordinary Gentlemen" roller coasters because he is too overweight, he becomes disappointed.
Split into simpler sentences: The Griffin family decide to travel to the Six Flags amusement park. When Peter is barred from riding "The League of Extraordinary Gentlemen" roller coasters because he is too overweight, he becomes disappointed.