This information is from OHRP.
Children who are wards of the state or any other agency can be involved in research that is:

• no more than minimal risk with permission from a guardian; 
• more than minimal risk but presents the prospect of direct benefit to individual subjects with permission from a guardian; 
• more than minimal risk and presents the prospect of no direct benefit to individual subjects, but generalizable knowledge (societal benefit) ONLY if the research is 
  --related to their status as wards, or 
  --conducted in schools camps, hospitals, institutions, or similar settings in which the majority of children involved are not wards.

The IRB must require appointment of an advocate for each child who is a ward, in addition to any other individual acting on behalf of the child as guardian or in loco parentis. 
 

• Research not otherwise approvable that presents an opportunity to understand, prevent or alleviate a serious problem affecting the health or welfare of children, but does NOT provide direct benefit to the subject or societal (indirect) benefit. The research cannot be approved unless the criteria in #3 are met and HHS Secretary approval is granted. 
   

  NOTE: The foster parent is usually not the legal guardian of a child in foster care. The social services department usually has legal authority for the child.