The methods to restrict purchases will vary depending on your device, please see below for Apple and Android methods

Apple: https://support.apple.com/102470  
Google Play/Android: https://support.google.com/googleplay/answer/7039872  

If a child will be playing the game, we have safeguards in place to limit accidental purchases, such as an age check gate before accessing such options. Additionally enabling these device-wide safeguards serves as an additional layer of support to avoid accidental purchases.