Starting daycare/school is always harder for the parent than the child, I think!! I am a 4 year old teacher at a daycare, and quite often the parents have a harder time than the kids. Just keep in mind that your son will greatly benefit from being a childcare! The main reason is the socialization skills he will learn. He will learn how to share, talk to and play with other kids, solve problems, independence, just to name a few. Look for centers with a good curriculum that teaches colors, shapes, numbers, ABC's, pre-math, and pre-literacy skills. This will also help him once he starts Kindergarten, since he will already have adjusted to being away from family for the day or a few hours.
Just keep in mind that it may take up to 2 months for him to fully adjust to the new environment, especially if he's used to staying only with family. It will help so much if you keep a positive attitude about him starting school!!!!!! I can't stress that enough! If you are nervous, then he will pick up on it and not want to go. If the teachers aren't patient enough to help him learn to share, then find a new school. A good teacher will show a child how to interact with other kids, not just tell them. Visit the school and meet with some of the teachers he will be with before signing him up. Make sure you are comfortable with the center. Ask about their discipline procedures, curriculum, operating hours, communication with the parents, naptime, sick policies, and anything else you feel necessary.
Remember, some changes take time for kids to adjust, so be patient. If he has one great day, then a sad day the next, that's normal. He will adjust and make friends, and you will have forgetten how nervous you are now!! Good luck!!