Wood.

C can't tell what species the firewood is. This is strange to me- I can remember not being able to tell the difference, but I also remember not being able to read. The oakness of oak is obvious, due to its weight and grain and the moss that grows on it. The pineness of lodgepole pine is also obvious, with the cornflake bark and the lichen (very different from moss to the untrained eye, I'm sure) and the abundance- they wanted to burn thirty years ago, and have died ignoble deaths instead.

Of course, my first word was "wood". I'd point at woodpiles on long walks with immense gravity and declaim: "Wood."

Which according to the mad science of children book I'm reading, probably means my father and mother did a lot of gesturing at woodpiles while saying "wood" in many different sentences.

Betcha C's first word was "phone". Or "wash". Sadly, it has been lost to science. The closest I can get is this excellent quote, "I called soap the word for butterfly. Or was that pants?'

According to one of those identity stealing Facebook apps, my most commonly used words in posts are "German", "poison", and "rain". I will have very strange children.