There are two ways by which you can prevent access to the top menu (Settings / Edit buttons)
By password protection
You can set up a password that prevents unauthorized access to Settings and Edit.
- Tap the Settings button.
- Scroll down to the bottom and tap on Add Password
- Enter the new password.
- Confirm the password by re-entering the password and tap Done
By Guided Access
You can use the Guided Access option of iOS to disable certain sections of the app screen and prevent them from being accessed or activated by the child. (Settings > Accessibility > Guided Access)
Click here to read How do I set up Apple's Guided Access to disable portions of my screen