just write a certificate of the relationship between father and son/mother and you can get notarized.

prove (center, No.2, bold)

This is to certify that XXX (you), (gender), (ethnic group), (ID number), this comrade is XXX (your father), (gender), (ethnic group), (provincial certificate number), the eldest son (who is the senior) is true.

this is to certify that.

(unit or department that issued the certificate)

(date+seal)