"Also my hands get bigger and smaller. Is that intentional to show being a child and grown up?" < yes
If you currently see the sister sleeping and waking with the sound of the music, you'll want to get to the source of the music. When the music gets more audible and the doll becomes sleepy, that's a sign you're on the right track. It also helps to remember what happened before this part, such as the walls unexpectedly moving and the way you could change the key/lock.