Adelaide, though she has a smaller role in episode 1, is one of the other leads of the story. She is 12 in the pilot/before aging up, so if you want to play her long term, I imagine her voice might change over time, though I'd rather the voice fit than be the most realistic in that regard.

Allow me to be very communicative and careful when discussing this: Adelaide is meant to be on the autistic spectrum. 

While I myself am not on the spectrum, a few of my very close friends are, and I would like to depict this part of her with a lot of realism and nuance. I am not requiring the actor to be on the spectrum to play this role, but please understand this as an element of the character, and one I want respected and taken seriously if you want to play her.

Adelaide is not particularly book smart and often struggles to emotionally understand other people. She is also genuinely sweet, fiercely loyal, and cares a great deal about those close to her. She is often very outspoken, emotional and loud. She can come off as a fair bit air-headed or naive. It is easy to mistake her as stupid due to this, but I like the idea Adelaide is often very perceptive, thoughtful, and good at remembering things that she is told if she feels it matters to remember for someone. 

Adelaide loves Chelsea and always recognizes how much effort Chelsea puts into their relationship.

Adelaide should sound high pitched and cute. Slightly naive without sounding like an actual moron. This might sound a little silly, but I like the idea she is "incorruptibly good". She wants to do the right things, and has a lot of care and empathy for other people, and no matter how she changes, that always remains true of her.