When DS was 3 and super into the endless string of q's I was torn between answering them and my sanity. A teacher once told me that not answering their questions and putting them off kills their curiosity and makes me less interested over time - but they hadn't met my kid - I was pretty good for the most part in answering them or turning them back around - what do you think, etc. but one day it was one why too many and I just lost it a minute and just said Zee! He looked at me like I was nuts and then got it -xyz - and laughed. It became a little understanding between us - mommy has reached the end of her question answering ability, please come back later!
The good news is his questions just get more interesting over time.
DeHe