For a short stay, you can get a feel for Vienna by following any of the three Rick Steves audio tours available from this website: https://www.ricksteves.com/watch-read-listen/audio/audio-tours/austria-germany. Especially the tram tour of the Ringstrasse could be a good way to start. As for activities, we don't know what your kids would like, but Vienna is especially rich in music, art, and architecture sites and activities. Since you are staying near the Prater, that's an obvious choice even though I didn't get over that way during a 10-day stay. At least duck into the back of St. Stephen's Cathedral; if this will bore your kids, you wouldn't have to pay to get in for a closer look; from the rear of the cathedral, you can get a sense of the grandeur. Do one of the famous coffee houses, and for other food, see if you can get expose your kids to some wiener schnitzel. Otherwise, let the kids research and each pick one.