I am in Vienna with my family for 2 days, what would you recommend?
What are you interested in? The Kunsthistorichemuseum (sp?) has one of the great art collections of Europe. The Stephandom (cathedral) is awesome. The Jewish monument on the old synagogue site is poignant. The Hofburg is interesting, especially if you're into either tableware or Empress Sisi. I haven't been to the Schonbrunn Palace, outside Vienna, but many recommend it. The Opera House is beautiful. Lots of nice parks for sitting and strolling. A famous amusement park north of the center that should appeal to kids.
Check out a guidebook (literally, from the library, if you can) and peruse the listings with your family. Pick a few major sights you'd all like to see, or give each person his/her top choice. Plot your course based on time, opening hours/days, and your collective priorities. Be flexible about weather, especially for outdoor activities. Allow time for strolling, cafes, and such to really enjoy your visit. And, as RS reminds us, "assume you will return."
If you don't yet have a guidebook, see also Rick's list of Vienna priorities. That list doesn't include the Prater amusement park, but I did enjoy it for a beer garden, historic ferris wheel, and good people watching on my last visit; kids would take more of the rides, of course.
The Ferris Wheel is called the Riesenrad made famous in the movie The Third Man.
I am sure the beer garden you refer to is the famous Schweizerhaus:
What are you and your familiy's interests?
I just want to second the recommendation for the Prater amusement park. It was a lot of fun to see the Viennese at leisure, and as a bonus you see more ethnic diversity there than in the city center. If you have children, they may also like the zoo near the Schoenbrunn Palace (I don't have kids, and enjoyed the zoo myself).
Suggestions greatly depend on the time of year. The Prater, for example, is a complete dead zone in the winter. There are also special family events/festivals which I can recommend, but need your dates.
I will be there 1st week in August