4yr old: Mummy when will I be as old as my big sister?
Me: In 8 years you will be as old as she is now
4 yr old (wailing): But I don't want to DIE!!!!

Also quite regularly:

4yr old: Mummy, when will I get to go on stage and hold the microphone?
Me: When you are in school you will get a turn too
4yr old: Mummy, why is everyone looking at me?!?!? Make them stop looking at me!!