I bought the Universe book as a present for E a few years ago. He lugged back the Nature encyclopedia a few months back when he spotted it. Both books contain mind-boggling contents that even adults may have difficulties comprehending.
Night after night, the boys descended on the daddy like wolves, hungry for knowledge. E, as usual, is ever so willing to feed their voracious appetites.
While it is not about turning them into walking encyclopedias, a curious mind cannot be cultivated without the introduction to a certain level of facts and understanding them. The kids continue to amaze us with their abilities to remember the details and ask the most fascinating questions. It's all about having the exposure and opportunities.