Where do Austrians go for summer vacation? It was always the question: shall we go to the mountains or to the sea this year? The preferred sea destinations of Austrians taking the car are Italy (special shopping flair) and Croatia (very clean sea). As for flight arrangements most Austrians like to go to Greece (room & breakfast on small islands), Spain and Turkey (best bargain for AI clubs).
The majority of the Austrians, however, prefer to stay in their home country and enjoy the mountains (called Sommerfrische) and the beautiful lakes. The Woerthersee is no. 1 in ranking of the most popular lakes in Austria, followed by the Attersee (coldest lake in Austria), the Wolfgangsee (favorite lake of my friend Rachel and her five children), the Grundlsee (surrounded by mountains) and the Neusiedlersee (sea of the Viennese).
As for kids, all the bathing lakes in Carinthia, like the Millstaetter See, the Faaker See or the Klopeiner See are warm and clean and the weather in the South is usually very sunny. Also the Roecksee area in Styria offers a lot for families, like the Styrassic park. the Zotter chocolate factory and the H2O-Therme for bad weather. For accommodation try the family hostels JUFA Tieschen or JUFA Leibnitz, the kids love it.
The Lake Neusiedl is very close to Vienna and a perfect weekend destination for swimming, sailing, wind-surfing and bicycling. There are lots of bicycle rentals available and the best bike route is between Podersdorf and Illmitz with many animals to see. My favorite beach resort is in Podersdorf, but families also like the bathing beaches in Rust and Neusiedl am See.