Steven French, professor of the Philosophy of Science at Leeds [and obviosuly much more knowledgeable than I about these matters] sends the following addendum to my response to my son's questions:
"This is just to say that [Ernst] Cassirer, as a neo-Kantian, directly responded to the challenge posed by QM [Quantum Mechanics] in his beautiful book Determinism and Indeterminism in Modern Physics (Trans. By O.T. Benfey), Yale University Press, New Haven, where he argues that it is not the concept of determinism that quantum physics bears upon, but rather the concept of *object*. Quite a bit has been written about that last point and, of course, about Cassirer in general in the past few years."