Children are often a mirror to our true selves. My daughter is fascinated by the world, and loves learning. She's a sponge for new knowledge. The only limitation is building up the layers of knowledge, to understand what you are trying to teach.
My 6 year old loves to learn about math, sciences, a few other subjects to a lesser degree, plus practical stuff, like driving/traffic behavior. He mainly likes biological sciences and astronomy, but some physics and engineering.
I don't know how much is innate and how much we fostered, but we read a ton with him from a very young age and made it into little quiz games and fill in the blank questions. He's always liked knowing the answers. My 3 year old is less interested, but I think she'll absorb a lot just by being around her brother. We do read to her, of course, but she chooses different books than the 6 year old does (and even did at 3).