You can prevent the child from deleting the app by disabling the iPad's home button. This can be done by using Apple's Guided Access feature, which disables a portion of the screen, as specified by you.
Tap here for more details : How to prevent the child from exiting the app?
For iPads and iPhones:
There is a setting that you can set up to prevent app deletions:
How to prevent app deletion on iPads and iPhones with Screen Time?