Illogical Questions

My daughter and I have some interesting conversations in the car. Not much else to do, while we are all strapped in but look, listen, and talk. That is, when we can hear each other above the noise of her joyfully babbling baby brother.

I'm having some difficulty answering some of her questions. I knew this day would come, but I had no idea how frustrating it would be for us both. I don't believe it's lack of intelligence on my part (I know why the sky is blue) and it's not because I can't phrase things simply enough or come down to her level. It's more because of the issue of logic. Or lack thereof in the mind of a 3 1/2 year old.

For example, we live near a small airport and often drive by the runways on our way to go pretty much anywhere. Lucy loves planes and helicopters, so we often point them out to her when she doesn't already see them coming. One particular plane was landing, and it looked like a very old World War 2 flyer. Our conversation went something like this:

Me: Look, Lu, there's a plane landing.
Lucy: I see it!
Me: Wow, that's a really old plane.
Lucy: Why?
Me: (long pause) Um, it's just old.
Lucy: (sounding like she's going to cry) But why is it old?

How does one answer the question of why something is old? Because it's old! I think I fumbled my way through the explanation that it was made a long time ago and has been flying for many years. Not sure any of that meant anything to a girl who can't keep straight the difference between tomorrow and last week.

Another similar conversation took place on our way home yesterday:

Lucy: Mommy, when is daddy going to be home?
Me: He'll be home in about 3 hours, honey.
Lucy: But when?
Me: After your nap.
Lucy: But when?
Me: Sometime around 6 o'clock.
Lucy: But WHEN?

These exchanges often frighten me. Lucy hates to be misunderstood and becomes an emotional ticking time bomb. We often have to find quick resolution or change the subject ("You want to listen to Veggie Tales?") to avoid making her cry.

As I have mentioned previously, I've often thought I took the wrong path in college and should have studied science because it appeals to me and makes sense to me. I've always believed I can answer my children's questions on things like why crickets make noise and why we see only part of the moon most nights and why some things float in water and others sink. But as prepared as I am for questions that make sense, I have no idea what to do with the ones that don't.

As for the question of when, I have helped Lucy make a paper chain that counts down the days until a big event (like Christmas or special visitors), and I let her tear off one link each morning at breakfast so she can count the number of days remaining. But explaining the passage of hours to one whose mind can't quite grasp the concept yet is still beyond me.

How do you answer the illogical questions?