I have joined Virgin Mobile however I cannot access anything deemed mature content via 4G. I have looked into the forums and the advice offered is parental controls are set "on" by default and can be disabled by accessing my account page and selecting :-
When I log into my account I am not presented with anything other than my mobile bill and some basic user settings. There is no option allowing me to change plan or devices. These settings are also not available via the mobile app.