On May 11, 2012, the VFS issued a new guideline for the interview process applicable to children under 7 years of age. According to the VFS :
Children under 7 years of age are not required to appear for a nonimmigrant visa interview at any Post in India. Such applicants may submit their visa applications through VFS. All other rules, requirements and fees for those under 7 years of age remain in effect. All applicants must include the following documents when submitting their applications:
The applicant's valid passport
A completed DS-160 application barcode
One 2" x 2" photograph that meets specifications; and
An HDFC visa fee receipt (with both pink and blue copies) for the current visa application fee
Note: Parents/guardians may also consider submitting the following documents: the parents’ U.S. visa numbers, information about the purpose of the visit and those to be visited in the U.S., and evidence of the applicant's ties to India. Visa issuance for those not appearing in person is not guaranteed. The Embassy/Consulate may in some cases, after reviewing an application, require the child to appear in person.
You can go to this link to fill out the form required for waiver for children under 7 years of age: Non Immigrant Visa interview Waiver form