In PokoPoko, there are in-app purchases that can be made to purchase in-game Items.
But you can set your device settings to avoid any accidental purchases.

1. Go to device settings
2. Select [Screen Time]
3. Select [Content & Privacy Restrictions]
4. Go to iTunes & App Store Purchases
5. Go to [In-app purchases] and select [Don’t Allow]

A detailed guide on how to disable in-app purchases is available here:
Use Restrictions to prevent purchasing on your iPhone, iPad, or iPod touch

If you do not want to disable in-app purchases but you want to enter a password every time you make an in-app purchase, please check the following guide.
Manage your iTunes Store and App Store password preferences