Why adult voices, and how they get there
Youthfulness in a voice is mostly energy, pace and a lighter timbre, not literal age. Sky, Nova and Puck are adult voices built from openly licensed recordings that carry those qualities; tagged youthful, they read as a bright teenager or a young adult, which is what most animation and learning content actually needs. This avoids the ethical and legal problem of children's biometric data entirely, and it also produces cleaner audio — adult recordings are simply better sources.