What is the difference between Bella's Lullaby and River Flows?

I downloaded was was titled Bella's Lullaby off Twilight Soundtrack's Profile on Myspace, but when i went to go look up the sheet music, I found River Flows, but many people said they WANTED that to be the lullaby but it wasn't, however when I listened to it on youtube it was the same as what I had just downloaded. Is it the lullaby? or is another song the lullaby?