Protection of Kids in Immigrant Detention Act or PROKID Act This bill establishes the Office of the Ombudsperson for Immigrant Children in Government Custody within the Department of Health and Human Services (HHS). The office shall ensure that if government detention of an immigrant child is necessary, that child is held in the least restrictive setting. The office shall also advocate for (1) the quick and safe release of such a detained child, and (2) a child who was detained with family to be released concurrently with a parent or legal guardian. The office's duties shall include (1) monitoring facilities with immigrant children held in government custody to ensure compliance with applicable laws and standards, (2) investigating claims of mistreatment and complaints against foster care providers, (3) reviewing contested decisions about the placement of an immigrant child, and (4) reviewing data from HHS and the Department of Homeland Security (DHS) relating to such children. The office may also offer individual case assistance to such a detained child who requires expedited processing or elevated attention. The office may also issue subpoenas with HHS approval. DHS and HHS must ensure that the office has the ability to conduct investigative and monitoring activities, including by providing unobstructed access to any detention facility with immigrant children. The office and DHS shall enter into a memorandum of understanding to coordinate oversight between DHS and HHS. The bill also establishes an expert advisory committee to assist the office and an interagency working group to identify and discuss concerns related to detained immigrant children.