What Do You Call That Thing That Princesses Wear?

Today's cute conversation after looking at a picture of a princess:

Erica:  Mary Lane, say "tiara."

Mary Lane:  "ta-ree-ah"

E:  No, say, "tiara."

ML: "ta-ree-ah"

E:  I said, say, "ta-ree-ah"...."Hey, it's a crown!"