Have you ever adopted a baby ,?
No i am not a fan of you assuming the  the parenting of another person's biological  child
So adaption dates back to what era?
I think Modern systems of adoption arose in the  20th century and tends to be governed by comprehensive statutes and regulations.
Any international laws on adoption?
Of course yes. but the prospective adoptive parents must meet the legal adoption requirements of their country of residence and those of the country whose nationality the child holds
Would you regard an adopted child as equal as yours?
Adoption
Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfers all rights and responsibilities, along with filiation, from the biological parent or parents. 
In many jurisdictions the adopted person's full original birth certificate is cancelled and replaced with a fabricated post-adoption birth certificate which states that the child was born to the adoptive parents. This deception, where carried out, may continue with the adopted person for
or religious sanction. Historically, some societies have enacted specific laws governing adoption; where others have tried to achieve adoption through less formal means, notably via contracts that specified inheritance rights and parental responsibilities without an accompanying transfer of filiation. Modern systems of adoption, arising in the 20th century, tend to be governed by comprehensive statutes and regulations.
History.
History Antiquity.
- Adoption for the well-born
While the modern form of adoption emerged in the United States, forms of the practice appeared throughout history.