The next episode of Little People, Big World on TLC featuring the Roloffs will air at 8pm on Sept 3rd, 2012.
It will be about the Australia trip the Roloffs took earlier this year.
TLC has the preview description:
Little People, Big World: Down Under - (LPBW Special #6: Australia)
With Jeremy away at school and Molly about to leave for college, the Roloffs embark on a once-in-a-lifetime trip to the land Down Under. It's an emotional journey when Zach brings his girlfriend and Jeremy returns to find the family has changed.