Eu encontrei a história. Está no Arquivo do Nosso Próprio e é " Para Ser Pequeno " por AvengerOfTheGods.
Harry Potter was severely abused. He is a little and afraid of what will happen when others find out. Snape is the first to care for him as Harry, not as the Boy Who Lived. Add in protective Slytherins, big brother Draco and a sane Dark Lord and you get a family that will stop at nothing to ensure his safety.