My youngest has the most questions, and she still asks a lot of questions...annoying at times. I don't know that any of my three really ever just asked "Why?", but rather questions.
Maybe around six years old, the questions were at their height, with things like, "Can babies contract communicable diseases prior to birth?". I typically just tell the kid to Google it, but that probably doesn't work so well at age three.
And then just weird observations...such as middle kid, at 6:30am, on the way to a sports tournament - "Did you realize that if you spell out numbers from 1 to 999, there isn't an 'a' in any of them?" Not really what I was thinking about at that hour, more like "Where is my coffee?"
I wouldn't worry if your three year old doesn't ask "Why?" much - I know my eldest didn't and she is doing just fine in college.
