The Family and Medical Leave Act (FMLA) is a federal law that requires employers to provide employees unpaid, job-protected leave for certain medical and family reasons, including personal or family illness, pregnancy, adoption, military service, family military leave, or the foster care placement of a child.
It is important to note that FMLA only applies to immediate family—parent, spouse, and child. While some states have expanded the definition of family many have not. So, a father could take FMLA leave to care for his children if their mother was seriously ill only if she is his spouse. If they were divorced or unmarried they probably would not be eligible for this benefit.
Also you may want to note that does not guarantee your same level of employment or your same position wth your company when you return from leave. If your position is a necessary one the company can fill it while you are away on leave. They only have to guarantee you some kind of job, not the same job.