The term Prussia was often used rather generically and synonymously with Germany. It could have been used to specifically designate the Prussian Empire only or it could mean just about any part of Germany except maybe Bavaria.
Based on some names I found at familysearch.org I suspect they were from Brandenburg. In there you will find the marriage and several children of Friedrich Wilhelm Charlet and Caroline Wilhelmina Witte. A few of the children seem to match. However, I suggest investigating the matter a bit more.