With a small child along, you might want to take a look on an apartment rental site (we use AirBnB) because it will give you more space, a kitchen to prepare what you may need for the baby and a chance to relax in "the other room." There are many listed, and generally for less than hotels.
Aside from the best-known sites (Stephansdom, Kunsthistorisches Museum, Albertina, Schonbrunn Palace etc.), you might find Haus der Klang (House of Sound) museum interesting. If you're a fan of the great movie, there's a Third Man tour available, including a walk through the sewer that figures prominently as a scene.
For archtecture, two suggestions:
..The Secession museum, built originally by Klimt and others as an expression of and home for their breakaway "jugendstil" in the late 1890s (contemporary and part of the movements that is known elsewhere as Art Nouveau, Catalan modernisme, etc.)
..Karl-Marx Hof, in the Heiligenstadt district, built in the 1920s by the Social Democrats in power at the time. It was intended as worker housing to replace Vienna's slums; it's a kilometer-long building (longest residence in the world) and one of the first to not only use only a small portion of the building site for the building, but also one of the first to incorporate laundromats, day care spaces, etc.