Treatment Family Care Services Act This bill requires the Department of Health and Human Services (HHS) to issue guidance for states about funding and establishing treatment family care services. Treatment family care services are structured daily services and interventions to address mental and behavioral health disorders, medically fragile conditions, or developmental disabilities that, among other criteria, are provided in a home-based setting to children who are less than 21 years old and enrolled in any Medicaid eligibility group. Specifically, HHS must issue guidance on (1) opportunities for states to fund treatment family care services through Medicaid, federal foster care and related programs, or other HHS programs; and (2) best practices for states to establish treatment family care services programs. The bill also requires the Government Accountability Office to assess and report on certain training provided to foster parents and other caregivers, including recommendations for improving state processes related to approval and oversight of the training.