For purposes of an employee qualifying to take FMLA leave for a family member, what may an employer require to confirm a family relationship?

the employee, parent of the employee's spouse, son or daughter, what may an employer require to confirm a family relationship? (See 29 CFR § 825.113) For purposes of confirmation of family relationship, the employer may require the employee giving notice of the need for leave to provide reasonable documentation or statement of family relationship. This documentation may take the form of a simple statement from the employee, or child's birth certificate, a court document, etc. The employer is entitled to examine documentation such as a birth certificate, etc., but the employee is entitled to the return of the official document submitted for this purpose.