This troper used to be the personification of this; he was cute,
innocent, and
oblivious to all evil. He delighted in riding his little scooter around the neighborhood, and would make friends almost instantly with anyone he met. He was homeschooled, and once he had finished his lessons, he would patiently sit around outside the other kids' houses, waiting for them to come back from school so that he could ask them to play outside with them. After awhile, said kids turned on him, and harassed him every day. But this didn't stop him from trying to be friends with them, and every day, he would come back and sit outside their houses and wait for them to come back from school to play. Eventually, he stopped playing with them. Instead, he stayed inside his house, and for months, only came outside to run errands with his mother, go to church, or eat.
That child is gone now.