In my humble opinion, the question "why" is the mother of all questions! It must be! Especially when asked by a wide eyed," innocent" kindergartner! They expect an answer... a satisfactory, correct answer. If you think this is easy, think again!
Just today, an almost five year old boy asked me "why is your pocket in your bottle?" that stopped me in my tracks! My brain trying to scramble, decode and formulate an answer in a split second! Don't ask what my reply was!
Anyway all I am saying, is you need a vivid, living imagination to take on the field of rapid fire queries in a kindergarten.. and beyond. Truth be told, the question "WHY" tags along through out our lives. And they aren't always right and straightforward. They tend to be rhetorical, difficult, and impossible to answer. Keeping a positive out look to life, and living in the moment helps to navigate the landmine of "whys"... Somewhat. Oh and never avoid them; face them head on! This not only helps build their confidence in you as their teacher but also builds their self esteem and outlook on life.