Chica doesn't have a canon voice to go off of, at least to my knowledge. The impressions that you can find online have a wide range, from sounding middle aged or sounding like a young child. For her voice, I hope to cast an actor that masters two aspects: To have a kid-friendly, welcoming voice in the beginning and also to have a creepier and scarier voice as the night goes on. However, that is just my opinion. Like Bonnie, I think you should experiment and find your own voice (literally!) Basically, just do whatever feels right.