Advice for database implementation
... save information about the children and several pictures and documents ...
... A friend is currently saving the data of over 70 kids in folders and subfolders on her device ...
... We need the database ... frontend ... easily add, change or display informations ... without any IT-knowledge ...

I don't say this very often, but in this case, I don't think you can - or should - avoid it.
Hire somebody that knows what they're doing, especially in the fields of Data Security, Web Application Security, and who knows their way around the General Data Protection Regulations (GDPR) - at the very least.
The rules and regulations around Data Protection and Security and, more importantly still in your application, Safeguarding, etc., are Legion and you DO NOT want to get on the wrong side of them.
Question: What's does your Privacy Notice say?
If your answer is &quot;What's a Privacy Notice&quot;, then you should not be touching this problem with a barge-pole!