The building shown in this image was the home of the first kindergarten held in the United States, which was founded by Margarethe Schurz in 1856 in Watertown, Wisconsin.
The description states:
First Kindergarten in the United States — founded by Margarethe Meyer Schurz in 1856 in Watertown, Wisconsin. Building moved from original site to Octagon House grounds in 1956 and restored by the Watertown Historical Society in 1957. Open to the public daily from May to November.
–There is an extensive and detailed history of this building recounted here.
Since the description states the dates of transfer and restoration, it is probable that this card dates from the 1950s.