NBS wants to know source of funds in boy’s small account

Dear Editor,

My eight-year-old son and I, his mother, have a bank account at the New Building Society (NBS). Just after his birth it was open to deposit all his monetary gifts he got from grandparents and friends for special occasions.  Recently I was told by a teller that I have to provide proof as to where I got this money from along with other documents. Why do they need all these unnecessary documents for a child’s account which has way below $100,000? 

Yours faithfully,

(Name and address provided)