This is my grandaughter in french?

There are a few ways to say "This is my granddaughter" in French, depending on the context and level of formality:

Formal:

* Voici ma petite-fille. (This is my granddaughter.)

* C'est ma petite-fille. (This is my granddaughter.)

Informal:

* C'est ma filleule. (This is my granddaughter.) *This is more common if you are talking to someone who knows your granddaughter.*

* Voilà ma petite-fille. (Here is my granddaughter.)

You can also use the diminutive "petite-fille" (little girl) to emphasize that she's young and cute.

Remember, the best way to say it depends on the context of the situation.