Four weeks drive through eastern europe from UK and back
 

Hello,
Planning a four weeks driving holiday with the family in summer through eastern europe.
Starting from UK and back.
Possible countries to visit if time allowed:
Germany, Czechia, slovakia, Hungary, croatia, slovenia, Italy, switzerland, Austria
We will book accomodations on route as we do not know how long we will stay in each place depending how much we like the place, etc.
Teenagers are keen on water parks...
If possible, based on your experience, can you please suggest places to visit and routes to take, etc.

Many thanks