Answer:
Sing me to a baby about to go to sleep.
What is black when it's clean and white when it's dirty?
I am used when you jump off a bridge for fun.
As I went over London Bridge I met my sister Jenny; I broke her neck and drank her blood and left her standing empty.
A little pool with two layers of wall around it. One white and soft and the other dark and hard, amidst a light brown grassy lawn with an outline of a green grass. What am I?
My days are numbered.