A free game can still charge real money for coins, lives and skins. These settings make every purchase ask first, on your phone and on a child's.
Block in-app purchases on an iPhone
Where to find it: Settings, Screen Time, Content and Privacy Restrictions, iTunes and App Store Purchases, In-app Purchases, Don't Allow
Screen Time's restrictions switch off in-app purchases for the whole phone. Set a Screen Time passcode that is not the phone's own, so the switch stays off.
Require verification for every purchase on Android
Where to find it: Google Play, your profile picture, Payments and subscriptions, Purchase verification
Choose Always, and every purchase through Google Play asks for your password, fingerprint or screen lock before it goes through. Anyone who knows the phone's PIN can also approve one, so keep it to yourself.
Approve a child's purchases from your own phone
Where to find it: iPhone: Settings, Family, your child's name, Ask to Buy. Android: Family Link, your child, Controls, Google Play
With a child's account in your family group, each purchase they try sends a request to your phone, and nothing is bought until you approve it.
