It depends on how small your business is. The federal Family and Medical Leave Act (FMLA) requires employers to give 12 weeks of unpaid leave in certain circumstances (and up to 26 weeks of leave for employees who need to care for a family member who was seriously injured while serving in the military). However, the FMLA applies only to companies that employ more than 50 people within a 75-mile radius. If your company doesn't meet these conditions, you do not have to provide leave under the FMLA.
However, many states also have family and medical leave laws, and these often apply to smaller business. So even if the FMLA does not apply to you, your state's law might. To learn more about your state leave law, contact your state labor department.
For more on the requirements of and exceptions to the FMLA, see Nolo's article Providing Family and Medical Leave.