Apple Store and iTunes - Enabling and Disabling Purchases

iPhone, iPad, and iPod Touch

Change your iTunes and App Store purchase options

• Go to Settings → Screen Time → Content & Privacy Restrictions
• Tap on iTunes and App Store Purchases and then tap on In-app Purchases
• Tap Don’t Allow on or off

MacOS

• Change restrictions in iTunes 

Family Settings

Apple offers buying and sharing controls for the whole family.  

1. Set up Family Sharing
2. Change the Ask to Buy settings