What's the best way to screen mirror phone to phone?

I’m trying to keep an eye on my kid’s phone when they’re at a friend’s house and I’m wondering if there’s a simple way to see their screen from my own phone. I’ve tried basic casting but it seems hit-or-miss-what works reliably without needing them to constantly approve it?

Most reliable options need consent or active connection approval. There’s no simple way to see their screen consistently without some cooperation.