Unssecured business loan-proof

This query is : Resolved

Querist : Anonymous

Querist : Anonymous (Querist)

26 August 2013 dear sirs,
I have started a small proprietory construction business.As I need funds I have talked to my sons to give me business loan of 5 lac each at 12 percent per annum simple interest to be payable at the completion of a particular running project or on demand (if urgently needed by them).My Sons are going to transfer the loan amts. in my business account through cheques.
My Question is should we execute a simple agreement for loan on 100 rupees stamp paper as proof if required my income tax department?
Is it necessary to get the abovementioned notorised by a notary public?

Is any other document required for proof?
pl respond soon
Thanks