Is there a special tourist promotion train fare for family travelling with children, travelling to/from Frankfurt to/from St. Johann in Pongau, Austria? Are the train tickets for children (under the age of 16) waived when travelling with their parents?
It depends on their age. Below two years old and on the parent's lap, they're usually free. From 2-8 there's a reduced fare. Above age 8, usually full fare.
In Germany children 14 and younger ride free when traveling with a parent. I did a timetable and fare check at www.bahn.de for Frankfurt-St Johann im Pongau and found the same to be true for that route.
Even better, if you book far enough in advance (up to 90 days allowed) at www.bahn.de, you can get an Europa-Spezial Österreich savings fare as low as 39€ for each adult or child older than 14.