Now 3 years old, Chase races his toy dump trucks through the family’s Dyer, Ind., home, a stark difference from when the paralysis of his right arm caused him to lose his balance. His parents remember the agony of watching him fall as he tried to walk. But a nerve transfer — a procedure that restored movement to his shoulder and elbow — and continued physical therapy has enabled him to use his right arm again, though he continues to build up its strength. In therapy he’s using a bat and knocking things down to strengthen his arm.