A “son or daughter” is defined by the FMLA regulations as a biological, adopted, or foster child, a stepchild, a legal ward, or a child of a person standing in loco parentis who is either under 18 years of age or is 18 years of age or older and “incapable of self-care because of a mental or physical disability” at the time FMLA leave is to commence.

The FMLA regulations provide separate definitions of “son or daughter” for its military family leave provisions that are not restricted by age.

Wage and Hour Administrator’s Interpretation No. 2010-3 (June 22, 2010) provides additional information regarding the definition of a son or daughter as it applies to an employee standing in loco parentis.