It is definitely important for your son to have interaction with other children his age. In fact, research has shown that peer relationships contribute a great deal to social development and to the effectiveness with which people function as adults. Indeed, the single best childhood predictor of adult adaptation is not IQ, not school grades, and not classroom behavior -- what matters is how the child gets along with other children.
If you like, you can begin your son's interaction with other children right in your own home by inviting children his age for short visits. Start with just one youthful visitor and his or her parent. Once your child has become accustomed to playing at home and in the homes of other children, he should be ready to participate in a playgroup. Many playgroups require parent involvement. Ask friends and relatives about programs that they use for their own children. Also, many churches and Y organizations sponsor playgroups.
You can find information on good early childhood programs by visiting the National Association for the Education of Young Children (NAEYC) website. The site also has a list of accredited programs that have met the highest standards.