First of all by undertaking this transaction none of the party to this transaction will face any tax implication i.e. no tax is to be paid on any gift transaction between relatives.
Also when your children will receive such amount from your mother they will not have to pay any tax in India.
You only need to keep in mind and prepare proper gift deed to document this entire transaction so if there is any enquiry you can answer.
I am assuming that your mother has never filed any income tax return since she has never opened a bank account so there might be an enquiry about receiving such a huge amount but that's normal and having a proper registered deed will help to answer them.
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