By far windows, windows lacks or doesn’t fully utilize features like full verified boot, sandboxing which means even if a program installs itself it still has to ask for permission for mic, camera, etc. Adding on to the issues even the programs themselves can be unsafe. Running a program that uses a memory safe programming language is pretty rare and a lot of vulnerabilities come from memory allocation and buffer overflow bugs. Android attempts to mitigate these issues by sandboxing every app, all phones ship with verified boot and full disk encryption, and usually have a memory allocator of sorts. And if you run a degoogled ROM you’ll mitigate the privacy issues by not having Google play services installed.
If you need some way to monitor these devices as an admin there are apps on android that allow this functionality, iOS has similar admin features.
edit: typos edit 2: added information
I hate to say this, but this is a blessing in full view. If people want the “freedom” to not take a vaccine because “risks, 5G mind control, whatever” then let’s let them. Life is full of risks and they need a wakeup call.