What lullabies could I put in my book?

I need at least one lullaby or nursery rhyme that my main character could be real fond of, even though she's already sixteen. The story is set in a futuristic fantasy world where games, nursery rhymes and lullabies, or anything child-related are just a mere memory. She remembers this one lullaby because she's not a real citizen of that world, so she sometimes just randomly sings them without knowing how she knew them.