Forgot the title of a favored fantasy book. Blindfolded Child with Deadly Powers

There exists a book that I have not read in years. In said book, the main character discovers they have deadly powers associated with their vision, and that since they are hard to control they must wear a blindfold for years. Their friend has animal taming powers, their father has the same power, and the setting appears to be medieval with serfs and farms. SPOILERS