I have a six year old who is obsessed with Love Story by Taylor Swift. She wants to perform it for us pretty much anytime we will let her. I've drawn the line at her coming into my room in the morning and waking me up by serenade.
I happened to see this version on be yourself, create art everyday and I really like it. It's a combination of Love Story and Viva La Vida by Coldplay, played on piano and cello. Be forewarned that it's quite long, and that it might just get stuck in your head all day.
And this is for Willa, to prove to her that the song is indeed about Romeo and Juliet, not Romeo and Julian: