how do you stop child from turning off location

Have a look at: Set up parental controls with Family Sharing on iPhone - Apple Support

- "With Family Sharing, the organizer can set up parental controls for children in the Family Sharing group. You can use Screen Time to manage how your children use their Apple devices." Screen Time lets you disable access to certain settings.

To prevent a child from turning off location services on their device, you can use parental controls or manage their location settings:

• Use parental controls
• On an iPhone or iPad, you can use Screen Time to restrict changes to privacy settings. You can also use Content & Privacy Restrictions to manage apps, content, and settings. 
• Manage location settings
• On an iPhone, you can go to Settings > Privacy & Security > Location Services and make sure it's on. You can also turn off location services for specific apps by going to Settings > Privacy & Security > Location Services, finding the app, and selecting Never. 
• Have a conversation
• You can talk to your child about safety and responsibility, and explain why you want them to keep location sharing on. You can also try to come to a compromise, like agreeing on when location sharing is required.