Legal adoption of children, severing all ties between the child and his/her natural family began in United States,1851, in Massachusetts. Spread from there throughout Western nations. Fostering has always been practiced thru-out history, and also by animals. but NOT adoption with all its broken filiation, legal fiction that the adoptive parents gave birth, and eventual sealed records. Child adoption is basically a modern social invention.
"The period between the 1st and 2nd World Wars saw the introduction of public adoption in many countries. ..."1920-1930 ... England, most remaining states of Australia and Canada, and most of England's sub-Saharan African colonies passed legislation during this period."
"By 1929, every state in the U.S. had passed some kind of adoption legislation. Legal adoption first appeared in Swedish and Norwegian legislation in 1917. The Danes introduced it in 1923, Finland in 1925, The USSR prohibted legal adoption in 1918 and re-introduced it in 1926.
"Not all countries had introduced legal adoption by the end of the Second World War. Several introduced it afterwards (e.g. Israel, 1960; Yugoslavia 1950; Ireland 1952, Netherlands 1956, Portugal 1967, Greece 1946, 1966)."
"The practice of adopting children in Western society was never very widespread. Adoptions were relatively few and far between and, in some countries were even prohibited by legislation. But at the beginning of the 20th century, and particularly since the First World War, adoption took a surprising bound forward ..."
Get yourself a copy of this book, ASAP: "Adoption, social work and social theory: Making the connections" by Tim O'Shaughnessy, Brookfield, VT: Ashgate Publishing.(1994).