My boss is doing research into how young children acquire logic with his three-year-old daughter.
My similarly aged son is at the "Why?" stage. Whenever I explain anything he will ask "Why?". The follow-up explanation elicits a second "Why?", etc. It is an effective mode of interrogation.
Following this method we swiftly reach the depth of my knowledge or the limits of my patience and I say, "Why do you think, Jake?", and he replies "I don't know!", and I say "Neither do I!", and then I go back to whatever I was doing and he goes playing with his trains or doing something dangerous with his little sister.
Sometimes Jake does not restrict himself to a single initial "Why?" and instead says "Why? Why? Why? ... Why Why!?", there-by saving himself the trouble of timing the additional "Why?"s in our dialogue, and I -- like to think -- identifying him as a passionate enquirer.
However, I am working on better, clearer, simpler answers. The challenge is to not use abstract or unfamiliar concepts in the hope that some of what he acquires is not just rote-learning.
Example: I stayed home to look after the kids on Monday while my partner went away for a two-day work-retreat. After we waved her good-bye Jake asked, "Where has Mummy gone?", and I explained that she had gone to "work camp", which was similar to the school camps that his older cousins sometimes attend.
Another example from breakfast that day:
Jake: Daddy, do you know that five and five is ten.
Daddy: Yes. And did you know that two and two is four?
Fortunately, at this instant I had just cut a passionfruit in half. I quickly halved a second one, lay the knife in between the two pairs.
Daddy: How many pieces are on this side of the knife.
Jake: One, ... two!
Daddy: And how many are there on this side?
Daddy whips away the knife.
Daddy: Now how many are there?
Jake: One, two, three, ... four!
Daddy: That's why.