From Cologne to Paris....best stop in between?

The direct Thalys train runs from Cologne to Paris in only 3.25 hours, so that doesn't particularly encourage stopping. It runs via Brussels, from where you can easily connect to the smaller town of Bruges/Brugge for an overnight. Whether you travel direct or split the trip in the middle, Thalys tickets are best purchased three months in advance of travel for the best prices.

You can choose any other city to visit with a slight detour by train. How to Look Up Train Schedules and Routes Online gives you the DB train schedule link and tips for using it.

Kids might find it fun to stop in another country - you could stop in Luxembourg City, it's about half way between Cologne and Paris and pretty easy by train: Cologne to Luxembourg is a about 3-1/2 hrs on the train, Luxembourg to paris is a little over 2 hrs.

I vote Brugge. It is a good contrast to Cologne and Paris, canals and old buildings should be attractive to kids. Take them on a boat ride round the canals. Then make them climb the 366 steps to the top of the bell tower (click here).
Click here for the official tourist site. Brugge is one hour from Brussels, with 2 trains per hour, an easy detour.

If they have had a surfeet of culture and history, take them to the Friet museum. Friets are what people from the USA mis-name French Fries, they are actually from Belgium.

Does that mean you have only one day to spend en route? If so, Bruges (and/or Ghent) is a good choice.

With more time. I'd probably start in Cologne, visit Bonn, (assuming no time for more of Germany) visit some combination of Amsterdam, Rotterdam, Antwerp, Brussels, Ghent, Bruges, Lille, Honfleur, Rouen, then into Paris. This reflects the way I travel, a starting point, a finishing point, and a sweep of places in between - while I'm in the area.

So much comes to mind. Take Trier at the west edge of Germany, where the remaining historic roman building marvels captured my attention. From the Black gate, a striking remnant of roman construction, free standing without adjoining walls, to the basilica remaining from the time of Constantine, the first christian roman emperor it just keeps coming. Roman baths, deeply entrench with tunnels, a exquisite palace of nobility from the fractured times when Germany held dozens and dozens of tiny kingdoms each holding sway over a few thousands citizens, I could have spent days there instead of just one long entrancing day. There are other cities nearby your route too, along with war-marked landscapes from both world wars. Take your pick but I like Trier.

Hi,

If it's in France before arriving in Paris, I'd say Amiens.

I love Amiens, too. If the kids want a change of pace, there's a bus to a nearby lake where you could spend an afternoon relaxing. Paddle boats are available, as well as boat tours.