I do not recommend the Prater Amusement Park, primarily because (compared to amusement parks in the US), the Prater is very sub-par and kinda sketchy (think a really bad Myrtle Beach boardwalk). Also lots of obnoxious teenagers are hanging around. My kids can't stand it.
Have you seen some of the recent posts I have made which include walks around the city?
There are also two really great kid-friendly festivals in the city this weekend:
Ernte.dank.festival - It is like a giant harvest/Oktoberfest bonanza. It is extremely family friendly with lots of really good food. I HIGHLY recommend this event. It takes place at Heldenplatz next to the Hofburg. https://www.erntedankfestival.at/?gad_source=1&gad_campaignid=22872796041&gbraid=0AAAAAqLqvjqZdQyXHfDEhhw1jVvVnHSkT&gclid=Cj0KCQjw8eTFBhCXARIsAIkiuOwhE6zP1RFMDde1i4sa4yYaECojhxQ2GL5-JtCO6Ex24joIgiLUk8YaAonpEALw_wcB
The Feuerwehrfest - Feuerwehr means Fire Service, so this is everything to do with the Vienna Fire Service, held in the very lovely Am Hof square. https://www.wien.gv.at/menschen/sicherheit/feuerwehr/feuerwehrfest.html
And I have a bonus idea - the Roman Festival at Carnuntum (https://www.carnuntum.at/en/romanfestival). Not too many know that Vienna was a major Roman military outpost. This festival, taking place at a reconstructed Roman site, is mega fun.
As for attractions, I always recommend Schonbrunn Palace for families. The zoo is great and the grounds are free. The maze and labyrinth (fee) are great fun for kids as well.
With museums, I suggest the free Wien Museum, which has descriptions in English and lots of hands-on activities for smaller humans.