Germany, Austria, Northern Italy Itinerary help

I caution you that the first day and last day of your trip will be wasted days. And every time you move from city to city is often another wasted day. You don't want the trip to be a blur!
Your itinerary is very familiar, however you are picking to stay in smaller cities. You are also choosing to not spend much time in important cities like Munich and Venice. Some of it the smaller cities may be a little quiet if the children are older. And I don't know where Halle is, as there are 4 such cities in the far north of Germany. It is obvious you are into mountain vistas.

My preferred general route would be to go to Munich, East to Salzburg, South toward Zell am See, over the Grossglockner High Alpine Highway and thru the Dolomites toward Venice. Then over to Verona, and up the motorway thru the Brenner Pass into Innsbruck. From there, you could go west toward Switzerland in Western Tirol where the valleys are deep and the mountains high. You could turn North and work your way back toward Frankfort--if that is your point of departure.