This is Walter's crush. Walt really wants her to like him, but she isn't used to other kids, doesn't speak baby and just isn't interested. On day one he learned her name and calls for her all the time. He climbed the tall winding staircase to her apartment and knocked calling her name, this is how he got in. He's been gaining an average of 5 words a day trying to impress her. Not sure it will pay off, but I'm impressed that he can now say "peanut" "good" "Elsa" etc.