This is a post-nuclear-war story where humans have mutated to have telepathic abilities. Institutionalized child (non-telepathic genetic throwback) has no volume control to his thoughts and "normal" telepaths hear his angry thoughts as mental screams and consider him a "monster."
At the beginning of the story you don't know he is a little boy; the nurses talk of him as a hideous monster that they loathe to interact with.
People still talk verbally. He is kept at a hospital and they want to euthanize him; his mother kidnaps him but brings him back telling them to kill him, "He's a monster!"
Maybe read in an anthology collection for high school English class - 1970's publication date?