Seigfried Line

I cannot specifically say where there are dragons teeth near the Ardennes (where the battle of the bulge was), but they are not restricted to there. There are lots of places all over Europe with dragons teeth and other old concrete fortifications. They are just not economic to remove. They are mostly overgrown and hidden in woods.
They even have some in Switzerland.

Also-We will be in the area of Cologne, Germany for a couple of days also.
Do you have a recommendation for a day trip on the Rhine?

From Cologne it's about an hour to Aachen (cathedral and throne) and, just across the border in Bocholtz, there's a footpath leading back to Germany. There's a bunch of teeth along it.

Thank you...we will be in Aachen so that is perfect.

For a day trip on the Rhine, take an EC train from Cologne to Bingen. At Bingen turn around and take the next MittleRheinBahn train north one stop to Bengen Statd and walk down to the river and get the KD boat north (down river). That will take you through the scenic Rhine Gorge. That boat ends in Boppard where you can get a train back to Cologne.

Timing would be: 8:18 EC 115 train, arr Bingen Hbf at 9:50, then MRB at 9:55, arr Bingen Stadt 9:57. The next KD boat is at 10:30. It arrives in Boppard at 12:50. MRB at 1:32 pm will get you back to Cologne by 4:01 pm, or you can switch to an IC train at Koblenz to get back by 3:05 pm.

That schedule is good until Oct 5. From Oct 6 to Oct 26, everything is one hour later.

As noted, prepare to do some hiking. They're usually located deep within forests, although there's probably exceptions. Anything closer to productive industrial or agriculutural land was likely removed long ago.

Sort of out of the way...but outside of Irrel, Germany; there is a museum that has restored some of the bunkers and emplacements of the Seigfried line... http://www.westwall-museum.de/

The teeth at Bocholtz are just into the woods about fifteen minutes from the town center -- less than ten from where I'd parked on the edge if the village.