Read a wide range of topics, read about things you are passionate about.
Gracious - read the dictionary! I did that growing up. Buy good dictionaries and when a child asks "What does this mean?" Tell, show and help them learn to use the dictionary. Personally, I would use a real one, as I think it helps with learning words.
Pick a subject at random, learn all you can about it. You truly never know when it can come in handy.