My husband I were foster parents. We had 73 + kids over the years. With a few exceptions, all of those kids went on to be successful in life. 
Most of the kids we had were teenagers, girls, who had blown out of other placements. Some stayed with us a few days but other kids stayed past their 18th birthday so they could graduate from high school.
It wasn't anything really that we did, it was that most of these kids were extremely resilient!  Survivors!
Many had survived horrendous childhoods filled with sexual abuse and/or physical abuse.
Some had good beginnings in their own families but due to circumstances ended up in the system.
20 years have pasted since our last foster daughter graduated and moved on with her life. She is a grandparent herself now and has done wonderfully over the years despite having come from one of the saddest backgrounds.
We hear from and see the "girls",many who are approaching 50's and are grandparents now. They had the tenacity to survive and thrive !