The Unnamed Baby is Luv and Bertie's crying infant child from Skyward Sword. Every once in a while, she throws a fit due to her missing Rattle. Bertie's job is to take care of her, and due to her crying, he is unable to sleep.
The baby's favorite toy is her Rattle, which a bird stole during the events of the game, mistaking it for food. This has caused major temper tantrums, making her and her father Bertie sleepless every night. Unfortunately, Bertie is unable to calm her, and her mother Luv is not able to do anything about it, since she sleeps through it. Link can retrieve the Rattle by using the Clawshot on the vines near the Waterfall Cave, then jumping off and landing on the bird's nest. Then, he must use the Gust Bellow to clean up the sand covering the toy. Giving it to Bertie cheers up the infant, and finally allowing a peaceful sleep.
Concept art of the Unamed Baby from Hyrule Historia