Small boy's two bald spots are showing some signs of regrowth. The new hair growing back is super fine, and is about 3/4 inch long now. The bald spots still look bald, even with the hair--and the one on the crown of his head is quite tan from the summer sun.
I'm sticking with my hypothesis that these bald patches were the consequence of the physical stress his body went through. Now that his body has renormalized to a large extent, he is regrowing the hair he lost.