Limiting Screen time on my Child’s iPhone
How do I setup limited screen time on my Child’s iPhone, and control from my iPhone ?
iPhone 8 Plus, 12
See this support document, however you will want to read at the bottom first to create Family Sharing if you wish to control things from your device. Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support This will show you how to set Screen Time restrictions after you have setup the Family Sharing.