The challenges that these families face are numerous. A lot of it also depends on the age of the children when they are adopted. If the children can be removed from the home at a young age the better chance the children have.
I used to live next to a family that adopted abused children and I have to give them a lot of credit. They faced a lot of tough times but always made it through.
I think that it is important to provide support for these families so that they are able to give these children the care and sensitivity that they deserve.
If you are referring to adopting children who have been abused in their previous homes, my thoughts are that the guardians of such children must be prepared to face the many post-traumatic effects that will surface in the child's behavior. They also need to be ready to be supportive, patient, and concentrate on making that child's experience at the adoptive home safe enough for the child to come back to society as a more peaceful individual, ready to trust, and take risks like every othe human being does.
Regarding adoption, I'd say that a family is often in need of a child especially when any of the parents are disable to give birth to. Sometimes, for the sake of poor and shelterless children, affluent families take help of adoption. However, it should be looked after whether the family takes good care of the adopted child or not. It is a humane responsibility.
Regarding child abuse, it is beyond doubt that, a child, when abused, is entirely shattered for good. S/he is broken up for ever. And this has an impact also on his or her family. It is very difficult to return to a normal life for that child.