Let me preface this by noting that our family will be staying in Hallstatt and will not have have access to a car so trailheads and cable cars will have to be able to be reached by train or bus from there.
Here is my fantasy: a high-country hike of no more than 5 miles up and back of moderate difficulty in the high country with splendid views of peaks and with at least one hut along the route. I am thinking perhaps one of the many trails in the Dachstein-Salzkammergt area reached from the Dachstein-Krippenstein cable car since the cable car is accessible by train and bus. One I have seen is the Heilbronn Circular Trail though it looks like it is heavily used. Vistas of mountain peaks or close-by massifs is a priority though alpine meadows and reflecting lakes would be icing on the cake. Want to be able to eat and relax at a hut either at beginning, along the route, or at the end. Much appreciation for your guidance in advance.