The ride from Nauders to Trento is fantastic. Very bicycle friendly and the kids will love it. Lots of castles along the way and lots of cows.
You can get a bus in Landeck. During busy times of the day, they hual a trailer too.
If I were to do it over again, I would ride from Landeck to at least the climb before Nauders. It is a beautiful road. But that last climb to Nauders is a killer, steep and narrow. I imagine you could get on the bus right near the start of the climb.
Actually if I were to do it over again I would start and end in Innsbruck. Take the Inn River bike trail to Landeck then the Adige to Meerano and then ride over the Brenner to Inssbruck. I rode down the Brenner into Innsbruck, I wish now I had ridden up too.
You might want to consider starting in Innsbruck too. There is a nice bike trail that goes from Innsbruck to Landeck though, it really ends somewhere around Imst where you need to take the road. It can be pretty busy and fairly steep for a young one.
When taking the trail from Nauders, stay to your left and you will see the sunken clock tower.
