2 days in Vienna (layover) - a crazy itinerary?

I vote, yes, very crazy, especially with two kids. I don't even think Salzburg is realistic given your time frame and given that you have to return to your hotel for the night (maybe if you stayed in Salzburg for the night, maybe). I would instead spend the time in Vienna: see the horses, take a boat/bike tour on/along the Danube, see the jewels, teach your kids about Marie Antoinette and then see the palaces where she grew up, eat some sacher torte, etc. There is plenty to do there with kids for two days.

Absolutely nuts. Really,you'll end up with 'some' of nothing. Pick one place and do it. IMHO

To understand the travel time that would be involved in something like this, click here and follow the train and car links.

Enjoy Vienna for 2 days. You'll remember something from that. Nothing but memories of trains if you try going anywhere.

I completely agree with the "some of nothing" comment. If you're going anytime May-Oct, you can easily fit in an excursion by boat on the Danube for one of your two Vienna days. But I have an even better suggestion: If you really want to squeeze one more city in with Vienna (and another country), my suggestion would be Bratislava (Slovakia). It's only an hour by train from Vienna and hunting down the various street art in the old city is a hoot; like the Napoleon leaning on a bench, or the worker watching people go by from his manhole, or the old guy bowing his hat to the ladies. If you keep your eyes open, you can even spot some of Napoleon's real cannonballs still embedded in a building's wall. There's even gruesome bones in the royal Cathedral that should please the 10 & 12 year-olds. Go early in the morning, come back mid-afternoon - easy and fun! People tend to forget how easy & accessible Bratislava is from Vienna... I really enjoyed my day when I went there.

A big vote for staying put in Vienna. But as to the previous post about bones in Bratislava, you can see the spooky skeletons in glass reliquary boxes in Vienna, too!
Just take the kids inside Peterskirche, right in the heart of town. Skeletons of martyrs were donated in the 18th century, removed from the catacombs in Rome, and dressed up in costumes of that period.

Thank you very much for all of the time you all took to reply! We've seen Vienna a few yrs. back, so this time around doing the "touristy" things aren't as much of a priority. That's why we were contemplating a little "crazy adventure" to elsewhere. Looking at the Bratislava option now - fantastic suggestion! Thanks again, everyone! :)

I do think trying to do the three is too much. Even more so since you are traveling with two young children. 4 years ago we stayed in Munich for 2 nights then took the train on to Vienna for three days. We opted not to do Salzburg as we were visiting these two areas at the end of our trip and it felt too rushed. I think if you try to do all three you might not remember what you saw because you would be rushing so.
Also, if you have never driven in that area, the traffic and parking is quite frustrating. Personally I would opt for Vienna and Salzburg. Good luck and happy travels.