Qualifications
Every state has different certifications, but you'll need one. A background check will be mandatory. After that, you can get started in preschool education as a part-timer, a volunteer, or an intern.
To qualify as a full-time preschool teacher, you'll need at least an associate's degree or a bachelor's degree in early childhood development (source). Some employers will ask for specific core curriculum credentials, and there are a slew of common licenses you're likely to need, like the CDA (Childhood Development Association), the National Child Care Association's Certified Childcare Professional (CCP), and the NAEYC (National Association for the Education of Young Children).
More importantly (well, the background check is probably more important), you should love kids and have great communication and instructional skills. You should like assisting and caring for others, be organized, be patient, and have a fun personality. If kids like you, you're probably headed in the right direction.