L.,
what Jennifer and Angelique have said is true. German Kindergarten (3-6 years old) do not focus on any acadmic things at all. It's a time for socialization and play. (Though I have read the other day somewhere that play is so important for kids as they learn so much and that if a kid did not have enough time to play they will lag of certain skills later on as they would have developed that during play time...) What a German Kindergarten (and then it depends on the specific school, too) does a lot more is working with crafts (use of siccors and glue and other materials) and they spend a lot more time out in their yard than I have seen other countries do (US and Italy specifically).
Having all that said what German parents do is find a Kindergarten in the area where they live as we don't drive our kids around a whole lot. Everything is done pretty much by foot. So if you end up in an area that has only on Kindergarten your kid will go there. If you are lucky you will be able to choose between a state or church lead school (protestant or catholic). They all cost the same within the county or city limits (generally about 60-70 Euro)as the government sponsors them (I read one place per child costs 6000Euro per year). In your case I suppose you would have to look for opening hours of the Kindergarten as we still have lots of them that are done at about 13.30. You would have to find something with longeer opening hours and that's where you will most likely end up with a place where a lot of kids go with German working parents.
And last but not least because he is not German the Kindergarten will only take him if they have space that they cannot otherwise fill as the Germans have a law that each child once it turns 3 has a right for a space.
If you have other questions we 3 did not hit on yet let me know--I live in Stuttgart, I have one son in Kindergarten and the other in the German School System, my husband is Army and we are station here in Stuttgart since last summer.
E.
P.S. If you decide to go with Kindergarten your son might not have certain acadmics (though you being a teacher you will be able to teach him things that you deem important, though you could just go German with you son wihle being stationed overseas) but he will learn to speak another language fluently--our older son speaks Italian because we put him into the Italian Kindergarten while being station in Italy.