Do you know much about adoption in the US?
I know about Adoption, but not really in US, Adoption is a process whereby a person assumes the parenting of another, usually a child, 
Are domestic adoptions cheaper than over seas adoptions?
Don't really know, but  the modern form of adoption emerged in the United States
That is interesting that it began in the US - do you know how many adoptions happen each year?
I am not aware of the number, Historically, some societies have enacted specific laws governing adoption; where others have tried to achieve adoption through less formal means
Are most adoptions done for infants or older children?
It is usually a child, from that person's biological or legal parent or parents,