A.,
As a child I lived out of the country twice. My father was in the Air Force and our tours of duty were both 3 years long. We lived in The Netherlands and Britain. Your kids are the perfect age to be going overseas and pick up a second language. At this age they learn to think in the language as well as english.
We traveled a lot in Germany and had a wonderful time. Bavaria was our favorite region to visit. Germany was still split at the time we were there, so due to security restrictions we were not allowed to travel to Berlin. Mannheim is in the Rhine river valley area in Germany. The Rhine is the river that feeds the German wine country. The area is known for it's spectacular scenery as well as all the castles along the river.
I think you will all have a fantastic three years and I hope you decided to go you will never regret it. Living in a country is very different than a visit. You really get a chance to see and explore all of Europe. Think of it this way in terms of distance Mannheim is about as far from Paris as we are from Denver. London isn't any further than Vegas is from us. You could easily be in Munich for the weekend. The Mediterranean is the best place to take an Easter vacation. With three years you have lots of time to really see things.
Merry Christmas,
J. N.