Under the GDPR you have the following rights towards the controller: the right of access (Article 15 GDPR), to rectification (Article 16 GDPR), to erasure (Article 17 GDPR), to restriction of processing (Article 18 GDPR), to data portability (Article 20 GDPR) and the right to object (Article 21 GDPR).
In practice, a request for information about the app is a short affair: I process no data about you or your child and can therefore neither give information about such data nor delete it – it does not exist with me. Write to me all the same if you have a question about it: kontakt@ausmal.club.
If your questions concern payments, invoices or your store account, please put them to Apple or to Google – that is where this data is held.
You also have the right to lodge a complaint with a data protection supervisory authority. The authority responsible for me is the State Commissioner for Data Protection and Freedom of Information of North Rhine-Westphalia, www.ldi.nrw.de (opens in a new tab).