I started using the Pi LLM app (by Inflection.ai) with my kids about six months ago and was completely blown away by how human-like it sounded, not just the voice itself but the way it expresses itself, the tiny pauses and hesitations, the human-like imperfections. It does feel like conversing with another human -- I've never seen another LLM do that.

(We mostly use it in car trips -- great for keeping the kids (ages 8, 12) occupied with endless Harry Potter trivia questions, answers to science questions, etc.)