If privacy is your topic, iPhones are out.
You could check /e/OS for example with Fairphone that includes parental control feature.
Your parents do not matter in this context and it would be shameful to use such features.

Avoid tracking apps and tracking in apps. Avoid big tech like Meta and use Signal instead. If your child is not willing to do without Tiktok, Insta and so on, you won’t prevent. You can only explain. Remember: Divice literacy is not media literacy

This. You can’t use your client, not on your phone nor on your PC. Therefore Tutanota was never a viable option

They changed some basics from Mull and decided to go other ways. That’s why I’m not using thus browser