How can I limit my child's in-game purchases?

Google Play

• In the Google Play app, tap the profile icon → Settings → Authentication to require authentication for every purchase.
• Set age limits under Settings → Family → Parental controls.
• With Google Family Link you can require approval for your child's purchases.

App Store

• Ask to Buy in Family Sharing makes your child's purchases wait for your approval.
• Under Settings → Screen Time → Content & Privacy Restrictions you can turn off in-app purchases completely.

If an unwanted purchase was made, you can ask the store for a refund; see Can I ask for a refund for a purchase? for details.