how do i delete an app permanently?

Apps are forever associated with the AppleID from which they were purchased - this applying equally for Apps that are "free" to download. TouchID and parental approval only control the initial purchase process; once purchased, Apps associated with your AppleID can be re-installed without further authorisation.

Your parents may find this information to be helpful with setting-up an AppleID for a minor - and in considering appropriate controls.

Apple for Kids - Official Apple Support

Help your child set up an iPhone, iPad, or iPod touch - Apple Support

Family Sharing and Apple ID for your child – Apple Support

Use parental controls on your child's iPhone, iPad and iPod touch – Apple Support

ScreenTime Restrictions might be helpful - limiting time that specific Apps can be accessed - or in preventing you from installing any Apps on your iPad. This measure will, of course, require that a ScreenTime Passcode is set by your Parents that you do not know.

• Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Adding Apps - set to Don't Allow
• Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps - set to Don't Allow
• Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > In-app Purchases - set to Don't Allow

More information on available ScreenTime controls can be found here:

Use Screen Time on your iPhone, iPad or iPod touch – Apple Support

Set up Screen Time for a family member on iPad - Apple Support

When you have already downloaded an app once, there is no additional approval by a parent or authentication needed. You could have a parent set up a screen time passcode on your device and prevent you from Installing Apps. This will remove the App Store from you screen and you will no longer be able to redownload the apps.