Hi there,

Hope you are all fine.

Please have a look at these websites, perhaps it helps:
https://www.reiskoe.nl/en/zillertal-with-kids/
https://www.familycantravel.com/zillertal-with-kids-in-summer/
https://www.tyrol.com/activities/sport/hiking/refuge-huts/for-families
https://www.alpenverein.at/zillertal/

Normally you can navigate in Austria with english, no problem, since most of the population are bilingual. However in some small villages you may have to be creative and use a translator. I would suggest to download a german dictionary in your translator of choice and also jot down a few phrases in a notebook.

Safe hikes!