"Because you didn't make yourself sick." Harry told her. "Someone else made you sick because they are bad and wanted to make us all sick." He hugged her, "Since you didn't mean to and they did it makes it their fault." It made sense to him, hopefully it made sense to a five year old as well.
"I doubt your Mummy and Daddy wanted a better girl than you. You are a wonderful little girl. And it's not your fault people got sick. I promise Ella. It's not your fault." If only he could convince her.