Both are about an hour and a half away from Munich Hbf by train. For the Garmisch trip, you could purchase a Bayern Laender ticket and the whole family travels on one ticket for 28 euro, all day.

http://www.bahn.de/i/view/USA/en/pri...r-ticket.shtml

For Salzburg, I don't believe a Laender ticket will cover you outside of Germany, but I could be wrong on this. You might be able to buy the ticket to the German border, and then buy another ticket into SZG.

You could also rent a car, but then would have to deal with traffic, and also would need to buy an Austrian autobahn sticker for your rental. A ten day sticker will run you Euro 7,90.

http://www.adac-shop.de/vignette_mau...duktliste.html

Can't help with the fests or parades, but it should be a nice time of year to visit. Generally the weather is warming up and the days tend to be pleasant.