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?
Absent a will saying otherwise all of your property is inherited by your next of kin upon your death. Your next of kin is your spouse if you have one. Your property includes your hard drives. Once someone is the owner of property they are usually free to do whatever they want with it, including giving it away.
After death property is passed to the spouse, then kids, then closest surviving relatives, then the state unless instructions are provided otherwise in a will.
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.
