This seems only change the subject of question from children to spouse. Does this change the nature of the question? I mean do your spouse automatically own your data when you die?
I assume data is property.
In this case the mother already had joint possession (through marriage) of her and her husband's property. While we refer to it as "his USBs" because he probably bought them and used them exclusively, when you're married they are legally owned jointly by you and your spouse.
One exception would be if he did the work on behalf of a company and the company paid for the USBs. Then the company could probably sue to have their property returned. Or if he had a contract saying that he had to delete the data after the contract ended, that could probably be enforced as well.