Military Families Mental Health Services Act This bill authorizes the Department of Defense to waive cost-sharing requirements for the first three outpatient mental health visits for certain beneficiaries of TRICARE Select and TRICARE Prime each year. Under the bill, active-duty family members are eligible for such waiver of cost-sharing requirements under both TRICARE Select and TRICARE Prime. Active-duty family members are dependents (e.g., spouses and children who are under the age of 21) of members of the uniformed services who are on active duty for a period of more than 30 days. Additionally, children who are under the age of 26 and are not eligible for an employer-sponsored health care plan are also eligible for such waiver under TRICARE Select.