Yeah kids on lower play only in school matches, upper they can do what they want (year 10 up) but generally play in school still. At the end of the day, get parental permission for any concerns however mild.
You want them on their own accounts really, it keeps them accountable if they do act out, they are the ones risking a ban etc. Ask your ISP now about it, see what they will require to open ports etc, it can take some time depending on how they process things. All our online stuff is only usable from one dedicated games user which helps keep it locked down outside of club times.