Were the sets of the 1964 movie "Mary Poppins" intended to look like a Broadway Show?

False

Most sets from those days were either done on a studio backlot or inside a studio. As it were, Carroll Clark and William H. Tuntke were nominated for an Academy Award for Art Direction for their work on Mary Poppins, which was, in fact, shot entirely inside of a studio. When you're working indoors, and using the technology of the time, you have the unfortunate effect of making the scenes look like a Broadway play due to the fluorescent lighting involved. However, as much attention as possible was given to make it look realistic.

According to page 11 of a research paper on The Making of Mary Poppins:

Like most Hollywood musicals throughout the 1950's, all of Mary Poppins was shot indoors, necessitating some fairly massive sets. The exteriors for Cherry Tree Lane and the park across the street were all housed in soundstage number three on the Disney lot, which had originally been built for Darby O'Gill and the Little People. The stage was the studio's largest, but it was still a tight fit trying to pack in everything that was needed.

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A painted backing finished off the set. "There was a mist over the whole thing," adds Tuntke, "and you could put a little smoke in front of it and it blended together with the mist on the backing. It worked out very well"