It would make sense to drive into the northwestern direction if you want wo visit Belgium.

On the German side, I recommend the Rhine and Mosel valley for picturesque villages and castles (Marksburg in Braubach at the Rhein, Burg Eltz at the Mosel).

For a romantic historic town, Monschau is the first choice. For history, see Trier (Roman heritage), Köln (Roman and medieval, the splendid cathedral), Aachen (the cathedral from 800 A.D.). All these places are in easy reach when you drive from Kaiserslautern to Belgium.

It is not Belgium, but from Aachen, Maastricht is in easy reach - a historic city in Limburg. In Belgium, the most attractive cities are (in this order): Brugge, Gent, Brussel and Antwerpen.

On the way back from Belgium, you may think about Metz (in France) or even Reims (if you care for champagne).

Do not hesitate to ask further questions if you have done some research on the mentioned places.

P.S. Forget Rick Steves for your trip.

I read OP's question that way that they plan to do several day trips from Kaiserslautern, and only one "longer" trip for 2 nights to Belgium. So I don't think you can put so much on your plate like Cologne on the German side if you plan to spend some time in Brugge or Gent.

Usual suspects for short day trips from Kaiserslautern would be Heidelberg, Trier or even Luxembourg or Strasbourg.

Coming back to Belgium. Is there a special reason why you want to go there. Traveller has already listed the nicest towns and cities to visit. But, Brugge is almost 500kms away from Kaiserslautern, so you will need 5 hours each way (without the stopovers traveller suggested above). Which adds up to a 1,000kms and 10hrs in the car. I am not that this effort is worth it for one and max two nights in Brugge. But that's for you to decide.

If Belgium is just the synonym for "something different", then you could go as well for two nights to Paris. The train gets there in 2.5 hours from Kaiserslautern, with 5 or 6 direct trains each day.

We wanted to go to at least one other country so yes something different was Belgium.
I thought Paris was a lot further than 2.5 hours by train.
I wouldnt mind a couple nights in Paris.

I am not looking at anything Rick Steves. It seems he send you to the most touristy spots.

Kaiserslautern is on the highspeed rail line from Frankfurt to Paris. And in France, the TGVs or ICE trains go up to 180mph. So, yes, it is a very simple and quick ride from KL to Paris. But only by train. With a car you will need much longer.
You can find connections and fares on bahn.com
If you book in advance, you can get discounted fares which are much cheaper than the walk-up fare, but are not flexible so you have to take a specific train.

You are awesome. We decided on an overnight stay in Paris taking the train. I wonder if they give militay discounts.

We also decided on a day Rhine river cruise. Not aure yet which company. Middle Rhine is best I read.

I am more excited to see our son than any part of the trip!!

Re: the Rhine cruise.

If you are coming from Kaiserslautern, the most scenic section is between Bingen and Koblenz. You can take the boat from Bingen to Koblenz (or a shorter section, but it should include the Loreley) and the train back. In addition, I would recommend to visit the Marksburg castle in Braubach and the cable car ride in Rüdesheim.

For details see:

http://www.k-d.de/english/home/