The only way I know of to lock a VPN profile onto an iOS device is by using configurator.app and setting the phone in supervised mode. Let me tell you: it is a pain in the neck.
As far as a desktop is concerned, I found the best way to do this is at the router. I use an ASUS RT-AC68 with the 3rd party Merlin firmware installed (based on dd-wrt). by following this guide you can enforce safe search on every device connected to your network.