You can be the strictest parent in the world but children due to social pressure or for whatever reason will end up with a mobile phone sooner or later, you can put parental controls on it but that will not prevent it from following the path of the majority at some point. Perhaps the solution is to demand not to have a phone or to teach them things from a young age that a phone can't project, but I'm afraid that nowadays intuition is easily defeated by technology. Sorry if my perspective is cynical.