Correct me if I am wrong, was the child in the hospital diagnosed with leukemia? Those diagnosed with leukemia lose their hair due to the radiation treatment (I believe). Anyways, the child's head looked as if it were shaved. I know this is minor, but it is a slip-up nevertheless.
For those with leukemia, hair loss can be a side effect of both chemo & radiation therapy. After the initial, temporary hair loss, when it starts to grow back...some patients choose to continue with the bald look so that their appearance remains somewhat stable, some let it grow back. We don't really know what phase of the disease this child was in, so the absence of a bald head isn't indicative of an error in the movie script.