train travel

If you are traveling up and down the Rhein, from Bonn to Mainz, you will be inside a single German state (Land). If you only use regional trains, there is a special regional passes you can use, called the Rheinland-Pfalz-Ticket, that will cover all five of you in the Land of Rheinland-Pfalz for an entire day, hop on, hop off, for only 25€. There are similar passes for other Länder (states) and for all of Germany. These tickets do not require pre-purchase; you can buy them the day of travel. If you want to travel between two points within Germany, you can get advance purchase (3-92 days) discount tickets, online from the Bahn, starting at 49€ for two adults, and the under 15 children would be free. There are also tickets for trips beginning or ending outside Germany starting at 39€ per adult. Again, children under 15 free.

Skip the Berner Oberland in March unless you want to catch the tail end of the ski season.

I don't know what sort of budget you are on but there are advantages to five people if you wanted to rent a van or even if you wanted to book a tour guide with a van or just a driver and a van. Being on the road opens a lot of possibilities and all three options can be less expensive than you might imagine.

"I will taking three grandchildren and daughter to Rhine River area of Germany,Paris..." The weather in the Bernese Oberland at that time isn't usually all that great. I think I'd stick with Germany and Paris, especially with just 12 days. For economy, the daypasses Lee suggests would be great for Germany. The Länder Tickets are explained here, as are two other daypasses for travel across state (Länder) borders - the "Quer Durchs Land" ticket (weekdays) and the "Schönes Wochenende Ticket" (weekends)- Copy and paste the link: http://www.bahn.de/i/view/USA/en/prices/germany/regional-offers-overview.shtml?dbkanal_007=L16_S02_D002_KIN0001_IS-regionalangebote-usa_LZ001 I'd suggest 5 days for the Rhine to visit castles and villages with possible outings to Cologne, Frankfurt, Mainz, Cochem (Mosel River) and Trier (Mosel River.) 5 days in Paris is about right as well. Extra time? Make a stop in Luxemburg or within France on the way to Paris. A well-located apartment is an ideal way for a family to have a relaxed stay at a great price. We enjoyed our stay in St. Goar at this 2-BR apartment a couple of blocks from the train station and with a view of the river: http://www.loreley-apartments.de/die_4_wohnungen_rheinblick_en.php The Rhine towns have many such apartment options. St. Goar's are listed here: http://www.st-goar.de/586-1-fewos.html Here's one in Bacharach: http://www.haus-schlossfuerstenberg.de/english/default.htm Contact local TI offices for the most complete info on apartments.