Train or Plane for travelling from Rome to Cologne, Germany?

Pricewise, you'll do best flying on a budget airline, either Germanwings or Air Berlin. Germanwings has direct flights and Air Berlin connects through Berlin. Book ASAP for the best fare.

If you take the train, do it overnight. It's a long ride. To get the best fares, make separate bookings at www.bahn.de ASAP (up to 90 days in advance). The cheapest Dauer-Spezial fare for Koeln-Muenchen is 29€. The cheapest Spar-night savings fares for Muenchen-Roma are 29€ for a reclining seat, 69€ for a bunk in a six-person couchette, and 79€ for a bunk in a four-person couchette. Couchette doors lock from the inside so your luggage is much more secure. Paying a little more for the extra space and comfort of a four-bunk couchette is well worth it.

It's a long trip, I'd fly. If you are only going back to catch your flight home, consider an open jaw ticket. You could fly out of Frankfurt, A'dam or Munich.

Thanks for the tip about an open jaw flight. However our kids have already booked the flight on British Air and it is locked in. I'm thinking the best would be to fly from Rome to Germany, visit the town where I come from for a few days (might even still find some relatives after 52 years), then maybe get a railpass for 3 countries (5days travel I believe) and see some more sights.