Under FMLA a family member is a parent, spouse, son or daughter.

A "son or daughter" is a biological child, adopted child, foster child, stepchild, legal ward, or a child for whom the employee acts as a parent (that is, a child for whom the employee takes day to day responsibility for care and financial support). - under age 18; or 18 yrs. of age or older & incapable of self-care because of a mental or physical disability.