August Itinerary Help -- last minute planning for 20 days in Germany/Austria

The Main Fest is along the river in Frankfurt on the 3rd. Rides, food, wine, music.

Going along the Romantic Road is going south and in the opposite direction to Berlin. Why not see some towns and cities going north from Frankfurt. There are tons of medieval, quaint towns all over Germany. Perhaps the Half timbered route or the Fairy Tale route would have some towns going towards Berlin.
https://www.deutsche-fachwerkstrasse.de/en/Homepage.html

Thank you so much! That's exactly what I was wondering -- if there were some equally lovely towns to visit that you won't necessarily read about in the big guide books. In your opinion, where might be the best town to stay the night on our way to Berlin?
Very good to know about the festival as well. We'll either stay closer and an extra day to attend or find a hotel far away from the festival if we decide to just be in the most restful place for the night.

For Frankfurt, look at Adina Apts. See if you can get one of the upper level, river side apts. Then you get a lovely view of Frankfurt. They have AC and have a little kitchen in the room. There are many parks here if you would rather just sit and play.

Because of the need to change hotels along the way, you have a difficult set of criteria from Frankfurt to Berlin. I would have flown a second segment right to Berlin, because there is so much to do there, and the hotel retreat will become familiar to your son. I should note that some years ago, we had a very hot summer visit, where both the Hilton Leipzig (on one possible route for you) and the higher-luxury Kempinsky Bristol in Berlin had air conditioning that could NOT keep up with the heat. We slept in our underwear in both hotels. OTOH, we stayed in a nice A/C business hotel with (not free? I don't remember) underground parking in Weimar, Dorint amGoethepark. I think your desire for small towns conflicts with air conditioning. I personally find changing hotels daily to be very stressful, but that's personal.

I would remind you that most countries in Europe don't fence heavily traffic-ed public park precipices in the way that we do in the U.S. My wife and I often note this when abroad. We did some of the Fachwerkstrasse last summer-note that it usually takes 15 minutes or more, each way, to get off the highway, into town, and find paid parking lots with scarce spaces. Such towns are typically surrounded by a banal modern (if low-rise) city, so even with a GPS, you have to look hard for the "Altstadt" signs.

I saw that you specified that you love driving long distances, but I don't see Berlin-Munich as a pleasure. Last year we took the train from Frankfurt to Berlin, not because we didn't want to see things (indeed, I specifically would have liked to see the palace in Gotha that we missed the year we did "the former East") but because it was efficient and effortless. Adults would like Dresden, but I don't know about a 4-year old.

Germany has vast numbers of wilderness spaces. Because we like the remnants of royal estates better, I'll mention two UNESCO WHS that you will probably have to choose between, the Dessau-Worlitz park, and the Bergpark Wilhelmshöhe in Kassel. Both of these are massive and highly (if, historically .... ) developed. But they have what you really need, which is Drive In-Drive Out with effortless parking. (There is an absolutely superb small art museum in Wilhelmshöhe. The watercourses are only turned on briefly twice a week.) I'd also mention the much smaller, but relaxing and enjoyable family (playground included) EGA Park Erfurt, which has a nice botanical garden, and parking (but we came on the tram, I think.)

If you choose the western route, anyone from Texas might want to see the church treasure (and the absolutely magnificent Altstadt) in Quedlinburg: https://en.wikipedia.org/wiki/Theft_of_medieval_art_from_Quedlinburg

I lived in Aschaffenburg and Wurzburg and here is a suggestion since you will be driving. Do not rent a car in Frankfurt unless you have done it before as it is not the easiest place to start driving. Take the train to Aschaffenburg and rent the car there. In Aschaffenburg there is a lovely castle named Johannesburg (sp?). There is also Pompeiigean (sp?) which is a replica of a villa in Pompeii. If you drive the old road (not the autobahn) to between A'burg and W'burg, just south of Haibach which is just south of A'burg is the village of Messpelbrun. It has a fairy tale moated castle that has been in the same family for 5-600 years. In W'burg visit the Prince Bishop's Residence. Be sure to see the Hofkirche on one end of the Residenze. Easy to miss if you are not looking for it. The Marienberg Fortress is ok but if time is tight skip it. The view of it from the town is more impressive that the view of the town from the fortress. From W'burg it is a short drive from Rothenburg, Milltenberg (sp?), and Heidelberg. And from there you can drive to Munich. You should be able to google all of these and see what you think.

Thank all of you so much! Exactly the kind of information I was looking for. Taking copious notes :)

The Romantic Road goes south from Wurzburg, so you really shouldn't plan to do that driving from Frankfurt to Berlin (a Northeast direction). Myself, I'd drive to Kassel, Magdeburg, and then Berlin. Those are decent roads, nice towns, and going in the right direction.

From Berlin to Munich, the best route is Leipzig, to Nuremberg, to Munich. It's 2-3 hours for each step of that trip with normal traffic. However, you are traveling in August, which is the vacation month, and traffic will probably be bad.

Munich to Salzburg is 2-3 hours drive also, but since you have the time I'd plan to spend some time in the smaller towns along the river. There are some excellent places to just walk the riverbanks and picnic.

From Salzburg to Innsbruck I'd detour to Kitzbuhl, but that's because I think it's beautiful. Innsbruck is often overlooked by tourists, and I don't know why; it's got a great historical center. Make sure you consider taking your son to the Red Bull Museum in Salzburg. It's full of airplanes and racing cars if he like that sort of thing.

I can't say much about Elmen, I used to ski in Ischgl, south of there, and that's beautiful country. If you think you boy will like it I'd suggest going over towards Garmish one day and taking the tram to the top of the Zugspitze. As long as it's clear you'll get tremendous views. If not, just get a local to point out some good hiking trails and enjoy the Alps.

For outdoors things to do, I recommend the following: The English Gardens in Munich, a walk around the old center of Nuremberg, Han-Donneberg Park (behind the castle) in Salzburg, the walk along the river in Salzburg, a visit to Lake Chiemsee, and the Zoological Garden in Magdeburg.

I do not recommend Dachau, it would be very hard on your son.

Last, I'll throw this out, because you're driving. I think the road from Salzburg to Chiemsee, to Bad Tolz, to Garmisch, is more scenic than Salzburg to Innsbruck.