Christopher,
Thank you for writing. The sixth and seventh Harry Potter operas are dramatic and heldic, respectively; they are intended to be heavy, and they are scored for adults only. The first two operas, both of which are light lyric, are the only selections of the seven in which children and teens are cast.
NB: I teach voice in SD, and I specialize in children. My music degree's focus was opera; I've studied voice capabilities fairly well. You might enjoy researching some of the newer scores for young voices; The Little Prince has an interesting score for boy soprano.
To be fair, I haven't posted my plans for the scoring of each book, where style and genre differences are concerned, on the opera's Website; these will contain the style and voice types for each opera. I hope to do this in the coming months; I'll have more score samples, including Harry's first aria for boy soprano, up then also.