How did that happen?

Cora was telling me about her day at school tonight during dinner. She was proud that she just finished worksheet #8 in grammar at school. She sat for a second and sighed wearily.
"(Sigh)....Adverbs. Long pause....They describe verbs."

What?

It just didn't register in my brain for a minute that my daughter had just used the word adverb, and that she knew what it meant. Not to mention verbs. Weird. She's growing up fast.