No. Anthropomorphic/Sentient/Talking animals don't, in and of themselves, make a film/book/TV programme/comic into a fantasy. 

**That said, we would consider them to be part of a fantasy if:**

 - They had been **[uplifted][1]** in some way (either by technology or magic)

 - Their speaking was **somehow fantastical** to the other characters.

The talking rats in Ratatouille would certainly fall into the latter category. There's no specific evidence of *how* they became intelligent but it's clear from the scenes in the film that animal sentience certainly isn't a normal feature of that universe.


  [1]: http://en.wikipedia.org/wiki/Uplift_(science_fiction)