Is there an parental control app that I can put on my iphone, that I can turn on when my 6 year old is using it?
Every PC apps seems to be for the kids devices.
iPhone 7 Plus
Settings>General>Accessibility>Guided Access. That allows you to configure your iPhone to only allow a child to use a specific app. See this support document, Use Guided Access with iPhone, iPad, and iPod touch - Apple Support
You cannot remotely turn off a device. If that is what you were trying to ask.
Is there an parental control app that I can put on my iPhone, but can turn off when I'm using it?
