Adoption is where someone legally agrees to act as the parent for a child, meaning they agree to provide everything that child needs to reach adulthood, including food, housing, and education. The first written records of adoption come to us from The Code of Hammurabi, which is one of the oldest written forms of law in existence. Written in the 18th century BC, this code spelled out the rights of adopters at length.
Ancient Rome used adoption extensively, with many of the Roman emperors coming to power by means of adoption. Here, adoptions led to a peaceful transition of power when there was no male heir. Roman citizens (the wealthy) under the Roman Law of Codex Justinianeus, would adopt an heir when one did not exist in a family. Families blessed with many sons often offered their extra sons as a way to strengthen ties with families. This also allowed for more wealth to stay in the family, instead of it being divided between many. As you can imagine, this only applied to sons, as women and girls had very few rights in the ancient world. Other civilizations in the ancient world would take orphans as slaves
This adoption between families lasted for about 1,000 years until the Middle Ages where a cultural shift emphasized the importance of blood relatives. This was, like most things in life, motivated by a desire to keep power and wealth in the family. Most major European countries discouraged adoption, such as France, Italy, and England.
Around the same time, the practice began to dedicate a child to the church. This male child would be given over to serve God, which would earn the family a higher reputation for having done so. You see this in the Bible as well with Hannah giving Samuel back to God for service. However, this division of wealth began to create an even bigger problem — orphans. Since medicine in the Middle Ages did not really exist, parents often died young, leaving their children to fend for themselves. And with no child welfare services, orphans often went hungry and lived on the streets. Monasteries became a haven for orphans, and the children for the most part, stayed there until they were of age to leave. This was exceedingly beneficial for the monasteries as they now had a form of labor, and they could spread their religion through this child-rearing.
However, the number of orphans began to grow, overwhelming even the monasteries. Thus, private organizations began. Most of the time, these private organizations just placed children in homes where they could learn a trade; however, the problem was that these children were often little more than slaves, forces to work to earn their keep. They were often forced to work for years until they could leave of their own volition. This tradition came with the English over to America.
At the time, children were not seen fully as having rights. After all, the infant mortality rate was exceedingly high, and many children did not live to see their fifth birthday. The death of mothers in childbirth from exhaustion, dehydration, infection, hemorrhages, and convulsions was almost as high. When mothers lost half of the children they birthed, many were aloof towards them, not wanting to get attached only to have their hearts broken. This also explains the looseness of the family system; it was too painful to get attached to your children.