Are you thinking what I'm thinking?

Let me set the scene...

Last week the girls are paining some bluebonnets and the conversation unfolds:

Sydney:  Ashby, are you thinking what I'm thinking?

Ashby:    I don't know Sydney.  What are you thinking?

Sydney:   Ashby, are you thinking what I'm thinking?

Ashby:     I'm thinking about painting.  What are you thinking about Sydney?

Sydney:  She pauses, puts her fist under her chin and says...hmmm...Iiiii'mmmm thinnnking                  abouuut...Santa Claus.  Ashby, are you thinking what I'm thinking?

Ashby:    No Sydney.  I told you I'm thinking about painting.

My guess is that Sydney wasn't too interested in what Ashby was thinking but just wanted to try out her new learned phrase, from where I don't know.