There are over 400,000 children in the foster care system, a fourth of which are waiting for adoption. The adoption of foster children has very minimal services required, the biggest fee being for the home study, which is required for all adoptions. Foster adoptions are handled by state, or public, agencies which primarily places older children.
Foster children come into the system from neglectful homes, the loss of parents or as runaways. The majority of foster children are in the system with the intent to reunite with their birth family. If the courts deem the birth parent unable to raise the child after a certain amount of time, then the courts will begin the process of terminating the parents' rights so the child can be adopted.
Some states have fost-adopt or legal risk foster programs that allow a couple looking to adopt an older child to foster a child who seems likely to be up for adoption. It's bittersweet because that means the child's parents seem unlikely to get their life together, but it's a helpful way for a foster family and child to grow together and adjust without the pressure that permanency but also with the hope for it as well. It can also establish a trusting environment for when news that the child's birth parent will have his or her rights terminated can turn to and appreciate. Adopters who have this option available to them and want to pursue it will need to pass a home study for adoption and foster purposes before being placed with a legal risk foster child.