When I was working in this field the children adopted were nearly all babies at about 6 weeks old. That has totally changed. The stigma of the unmarried mother, which caused girls to give up their babies for adoption, no longer exists; so those who are put up for adoption now tend to be older (or sets of siblings) and have very often already had a troubled existence.
Also, some are the children of drug addicts and are physically damaged by this.
Adopters take on a huge challenge - and the help received from Social Services is, in my experience, minimal to non-existent. The adoptive parents are often taking in very very damaged children; children whom professionals struggle to deal with. But the adoptive parents are expected to deal with this with only minimal support. And some of these children struggle in a normal family environment, because they do no have the emotional skills or the ability to trust others because of their traumatic experiences.
It is a very difficult balance between the rights of birth parents to be given a chance to make a go of it; and the need for the child to find "forever parents" quickly before too much damage has been done.
It is imperative that proper intensive support is given to adoptive parents to help them provide this essential service.
The children who fall through this system can be a huge drain on the public purse in the future, sadly often via drugs rehabilitation services and the prison system. And the emotional damage to the adoptive parents who "fail" is enormous and often takes years to overcome.
Another example of government failure to value preventative work.