Here is a walkthrough on how to limit how long your child is on their phone a day and how long they can use each activity. Using Apples new iOS 12 ScreenTime feature.
Some of the great features include:
Downtime lets you restrict certain activities, or all activities, on the phone based on just time of day. If your parenting style includes no technology after 8pm or something of the sort. This feature helps you enforce that rule. Once you set it up, in order to open those apps you would need to type in the restriction passcode that the parent would have setup.
App Categories by usage
Apple has also empowered the parents to enforce a rule like you may only play games on your phone for an hour a day. By creating a usage restriction all game apps could be blocked after an hour but still allow other apps to work as they normally would.
Overall a big win for parents.
We all intuitively know that these devices are incredibly addictive. This allows parents to thread the needle of allowing them a phone but helping to prevent addictions. Which by the way as parents we can lead by example by setting some restrictions for ourselves as well. If you are really serious, have your spouse be the one that knows the code.