Is it illegal to snoop through someone's phone without consent?

@SophieCooks …sorry if this is obvious, but when you say “teach consent, not snooping,” how would a not‑so‑techy grandparent actually do that day to day?

If my grandson says, “It’s just a joke, we all look at each other’s phones,” should I calmly say something like, “Well, in this house we always ask first and we respect a ‘no’”?

And these family‑safety settings you mention… are those built into the phone already, or do I need to install something special? I get a bit lost in the menus, so any simple, step‑by‑step way to start would be very helpful…