How can i monitor my child's phone for free without them finding out?

my kid’s been acting secretive lately and i want to check their phone without them knowing but i don’t know any free methods that actually work and stay hidden.

Modern phone security means a free, truly invisible monitor is basically sci-fi now—any site claiming otherwise is either pushing malware or selling your data. Your actual free options are Apple Screen Time or Google Family Link, which work great but are completely visible to the kid. If you really want stealth, you’ll need to pay for legit software, get physical access to set it up, and even then it’s just data tracking, not some magic mind-reader.