20 CFR 222.58: When a child is living with an employee.

A child is living with the employee if the child normally lives in the same household with the employee and the employee has parental control and authority over the child's activities. The child is considered to be “living with” the employee while they are living apart if they expect to live together again after a temporary separation. A temporary separation may include the employee's absence because of working away from home or hospitalization. However, the employee must have parental control and authority over the child during the period of temporary separation. A child who is in active military service or in prison is not “living with” the employee, since the employee does not have parental control over the child.