you can go to this website. There are two different names you should be looking for. First, CASA - Court Appointed Special Advocate adn the second is the Guardian Ad Litem. They work hand in hand with your Local Department of Social Services and Foster Care Families. They are also done by County. Depending upon which state you are from will determine the name that they go by. Try the link above and it should help direct you. If not, then call your local county clerk of courts office and ask them who you should contact to become a volunteer Guardian Ad Litem or CASA Representative. You should note that these are volunteer positions. If you are seeking a paid position, they typically are already attorneys.
Good luck.. And, you will find that it is a rewarding opportunity. You do have to take a course and get sworn in by a Judge. You will also have to go through a background check, be interviewed and sign a contract. This is something that the courts take very seriously. You will be assigned by Court Order to represent the child in each case. You must follow through with your promise to advocate for that child.
I love being a voice and having a say in either bringing a family back together after things have been fixed, or at least making certain that the child is placed with someone who will take great care of the child.