The issue is who controls the MDM profile. In the case of these apps it's the app developers instead of the parents. So by using it, you're giving some complet

The issue is who controls the MDM profile. In the case of these apps it's the app developers instead of the parents. So by using it, you're giving some complete strangers access to snoop on everything in your child's phone. Even if you trust the developer not to abuse that, you're trusting them to keep their own systems secure and to not hire an employee who might abuse it. We know how that worked out for the NSA where they had people using their surveillance programs to snoop on exes. If you want to use MDM to manage your child's phone, the way to do that is with a service where you manage the MDM yourself like a company would do with their fleet of phones, not to hand the keys off to an untrusted third party.