This Dwell article highlights some cool "Tiny Homes" for families (usually with one child). The photo above is of a 607 square foot home in Manhattan.
That's a bit smaller than the average 818 sf home size in the UK, which has the smallest home sizes in Europe. The average American home is 2300 square feet - 1000 sq ft larger than 1973 (even though the average household size has decreased from 3.01 persons to the current record low of 2.54 persons over that same time period).
Australia's houses are 2,217sf, about the same size as American homes.
Apparently Cliff Clavin wrote this post.