Answer:
Lovely and round I shine with pale light grown in the darkness a lady's delight.
I am a rock group with four members. All dead one was assassinated.
A piece of paper that takes most people 3 or 4 years to get.
Send poorly behaved children to me and let them sit here.
Sometimes I am white, sometimes I am dark. Most people love me. What am I?
No matter how little or how much you use me, you change me every month.