بسم الله الرحمن الرحيم
When your principal amount is deposited in the bank in good quantity then you shall not be termed poor in case your business falls short. You may withdraw your principal amount from the bank in the same way as you withdraw your interest money from your saving account and fulfil your needs.
This excuse cannot make you eligible for taking interest money and use it. If your business has fallen short then you can start any other business and fulfil your needs. Interest is haram and malice, one should always stay away from it. It is also not lawful for you to deposit amount for your children’s future and use the interest from it.
Allah knows Best!
Darul Uloom Deoband