Ok, thanks @BluePhaze.
You know, I'm using Flash CS6 to design my sprites. I don't know if you worked with Flash sometimes, but the way that Flash export the images as Sprite Sheet is quite bad. Leave too many blank spaces in the edges. Flash generates disordered sprite sheets.
My procedure is to export from Flash my animations as a png sequence and import to C2 as a frames. Doing this procedure with the project I'm testing now, I can see that C2 (when export the project) generate sprite sheet for every object, as you say. But this sprite sheets are disordered because the different images of the animation have different sizes.
When I import an sprite sheet to C2 I have two options:
1. Import an sprite sheet where all the images have the same size. Like this, after I can cut in e.g. 3 columns x 4 rows. Of course, to do this, first I have to transform, in some way, a disordered sprite sheet into a ordered sprite sheet (same size in all the images).
2. Import a disordered sprite sheet and cut the image that belongs to the frame. And to this for EVERY frame!
Doing in my way I only need to import png sequence and after crop the images (as a recommended practice). If this procedure doesn't affect the size of the project, in fact, in the end the result is the same.
Sorry for my long explanation...
What do you think? It's better if I continue with my way of importing?