Prepositions

We were driving along the freeway on our way to our friends' house and Sam must have seen a road sign because she said:

Tee-oh.  That spells "to," right mommy?

Me:  Yes.

Sam:  What does "to" mean?

Me [fumbling]:  "To" is like when you say, "we can go TO the store and you can point TO the dog, and you can talk TO somebody."  It's an action towards something.

Adam:  It's a preposition.

And because I talk way too much, I continued:

Right now we are going TO our friends' house.  When we arrive there we will be AT their house.  Right now we are ON the freeway.

And Sam said:

And right now we are IN the car.

Pretty smart, that kid.