Dear Sascha Cartwright
Thank you for posting in the Microsoft community.
You can define your installation of new programs for Windows through the registry.
This way your child can't install new programs at will, after all you can't individually define what browser program it installs.
Press WIN+R and type REGEDIT.
Locate:
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\Installer
If there is no Installer key, you will need to create it manually:
Right-click on the Windows folder, select New > Item and name it Installer.
Create and modify the key:
In the right window, right-click and select New > DWORD (32-bit) Value, name it DisableMSI and set the rule:
A value of 2: Completely disables the installation of all applications.
A value of 1: Only installations allowed by the administrator.
A value of 0: Enables installation (default value, no restrictions).
(Recommended setting is value 1)
Close the Registry Editor and restart the computer for the changes to take effect.
Disclaimer: Modifying the registry or workgroups is usually geared towards advanced users, administrators, and IT professionals, and it can help fix some problems, however, improper registry modifications can cause serious problems. Therefore, please make sure to strictly follow the steps below. For further protection, make a backup of the registry before modifying it. For more information on how to backup and restore the registry ref:
How to back up and restore the registry in Windows - Microsoft Support
Best Wish
Shawn.Z-MSFT | Microsoft Community Support Specialist