Ok I’m genuinely curious about your opinion on this disturbing matter

I saw a documentary about kids with mental problems. One of them was a girl aged 9-10 and she’d molest and take photos of her younger 4 year old cousin. The parents were saying she was just a child doing normal child stuff (since children do sometimes experiment). But the psychiatrist said she definitely had issues.
Would you say it’s normal or not? I feel like this isn’t something normal children do tbh.