A copy / paste from the affidavit of Birth Certificate that I'd used from a friend of mince. Had to scrape off from a pdf file so sorry about wrongly formatted texts. Overall this could be taken as a draft only and your folks in Nepal can work on it. Don't take it as an official template. This is what I had used. My friends had used different format and it still worked. 

Notary Public Dispatch No. XXX

Affidavit made by

Mr. FATHER’S NAME and Mrs. MOTHER’S NAME

We, the aforesaid deponents, FATHER’S NAME, bearing the Nepali Passport No. XXXXXX and MOTHER’S NAME, bearing the Nepali Passport No. XXXXXX, the residents of House No. XX, Ward No. XX, Proud Nepali Marg of Mirchaiya Metropolitan City in Siraha District, Janakpur Zone, Nepal, do hereby solemnly affirm and declare as follows:

Whereas, I, the aforesaid deponent, FATHER’S NAME am father and I, MOTHER’S NAME am mother of the APPLICANT. We are the parents of APPLICANT. 

I, the aforesaid deponent FATHER’S NAME, the father of APPLICANT am XX years old and similarly I, the aforesaid deponent MOTHER’S NAME the mother of APPLICANT am XX years old at present.

I, the aforesaid deponent FATHER’S NAME was present at the time of birth of my son, said APPLICANT who was born on 01 JANUARY 1975 at Lahan Hospital in Lahan Metropolitan City in Siraha District, Nepal.

Deponent: Deponent:

Signature: Signature: 

Name: MOTHER’S NAME Name: FATHER’S NAME

(Mother of APPLICANT) (Father of APPLICANT)

Date: Today’s Date Date: Today’s Date

Schedule-6

(Related to Sub-Rule (5) of Rule 17)

We, deponent, FATHER’S NAME, bearing the Nepali Passport No. XXXXX and MOTHER’S NAME, bearing the Nepali Passport No. XXXX, the residents of House No. XX, Ward No. XX, Proud Nepali Marg of Mirchaiya Sub-Metropolitan city in Siraha District, Janakpur Zone, Nepal, do swear in the name of God/solemnly affirm and declare that the content of this document is true and correct. I shall personally be liable under law in force, if the content is found otherwise.

Signature: Signature: 

Name: MOTHER’S NAME Name: FATHER’S NAME

(Mother of APPLICANT) (Father of APPLICANT)

Date: Today’s Date Date: Today’s Date

Schedule-7

(Related to Sub-Rule (6) of Rule 17)

The aforesaid applicants (deponents) Mr. FATHER’S NAME and Mrs. MOTHER’S NAME, known to me on verification of the submitted documents and it has been found that their personal details are found to be true and correct. I hereby verify that they have taken oath and signed in this document in presence of me on the date of TODAY’S DATE

Signature: NOTARY PUBLIC

Name: NOTARY PUBLIC

Date: TODAY’S DATE

Certificate number of the Notary public: XXXX

Date of expiry of Certificate: XXXXX

Seal of the Notary public: 

Also, another similar source:   

http://www.trackitt.com/usa-discussion-forums/i485-eb/987526277/bc-affidavit-sample-new