First off, bravo to you for taking these kids in. Obviously you realize they just need love. Secondly, I'm surprised the court system hasn't ordered counseling for the 3 yr. old. Not only did his world just do a 180, he's probably not able to express all his questions, feelings, concerns, worries like an adult would. He DEFINITELY needs counseling. Just to deal with the trauma of leaving home, if not for his current behavior issues.
Also, his behavior sounds like it could easily progress into Self-Harm if not dealt with soon. What he's doing is basically destroying (picking at, gougeing out, etc) something to make himself feel in control of something. Older children and teens have been known to do these things to their own bodies because it gives them some, albiet not much, control of their own lives. Or they'll do it for attention. I think this little guy is asking for special attention....he's getting it now negatively....but he needs positive attention too. One on one with a therapist would help tremendously.
If you have temp. custody, you should have Medicaid, and TONS of resources available to help you find counseling for him. Does he have a CASA (Court Appointed person that stands up for him in these situations)? You could contact him/her for assistance. Or talk to his caseworker at children's services. That's what they're getting paid for.
Whatever you do, please get some kind of counseling for him. Even regular visits/playdates with a pastor/priest would help him release some of his attention seeking behavior.
Good Luck to you and God Bless!-A.