arXiv, not QrXiv.
arXiv is a free distribution service and an open-access archive for nearly 2.4 million scholarly articles in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics. Materials on this site are not peer-reviewed by arXiv.
In my experience, there’s always a way around parental controls on these devices and if there isn’t, there’s always a way that your child will subvert them in other ways.
Half the time it’s a well-intentioned and ignorant adult providing them the means.