Daniel Kerner sits in his Portland hotel room, laughing as two characters argue in the film "Jimmy Neutron: Boy Genius" and moving in time to the music. Hair is growing over the scars on his scalp, where Oregon Health & Science University doctors last month injected brain-making stem cells. It was the world's first such procedure, his doctors say, a risky and experimental trial to fight Batten disease, the brain-wasting illness killing the California boy. In the four weeks since, his parents say, the 6-year-old has grown more lively each day. The milestones are small: More smiles, more eye contact,...