For my case I did the following because I had received RFE for a birth certificate.

Submitted below two separate documents:
1. A letter from Madar Village Development Committee that I, Kichhu Dada, was born 1975 and so and so were my parents (this document was dated 2004). This document was in English.(If it was in Nepali, I would get an official English translation).
2. An Affidavit, in a plain letter pad, signed by my mother and father, stating that I was their son and I was born 1975. This Affidavit was notarized (i.e. a Notary Public stamped and signed that letter - which basically formalizes an Affidavit).

What are the documents we need to produce for both #1 and #2?
I am in same situation (was born in Nepal in 1980) but never took the birth certificate and now we are Indian citizens with Indian passport