Finding Alternatives to Mass Incarceration: Lives Improved by Ending Separation Act of 2021 or the FAMILIES Act This bill establishes a federal statutory framework to divert certain defendants who are parents or caregivers away from prison and probation and into a comprehensive support services program. At the federal level, the bill establishes and provides funds for the comprehensive support services program, or FAMILIES Program. The bill authorizes federal courts to sentence a parent or caregiver to participation in the FAMILIES Program as a condition of supervised release or instead of probation or prison. At the state level, the bill funds grants for states to replicate successful state parenting sentencing alternatives programs that have the potential to keep parents out of prison. The bill also provides funds for a study on the effects of incarceration on children of incarcerated parents and for training district court judges to carry out the FAMILIES Program.