I have always recommended DNS control at the router as a first layer of parental control protection in the home. See previous post about Home Network Filtering. DNS control is also good for individual devices when they are away from your home network. You can set the DNS servers for each individual network that the device uses, but then you have go into the settings each time a device connected to a new network. Ideally, you want to force the device to use your chosen DNS for any network it uses to protect the device with filtered servers like Clean Browsing or OpenDNS Family Shield. Cleanbrowing now has their own app and an app to override the DNS settings on Android is available as well.