In a Static IP network the IP never changes.
In a Dynamic IP network (Like Virgin Media) you will get an IP for a set amount of time.
Virgin issue your device with an IP that last for 7 days.
Your Device (Superhub, Hub3, or Router) gets that IP and then after having it for half the time, it will ask Virgin if it is allowed to have the IP again for the same length of time.
So, First time you get an IP your router has it for 7 days, 3.5 days later it says "Can I keep it", Virgin network says Sure, and now it's good for 7 more days. It will repeat this forever.
So. Assuming you know exactly when your router last asked for that update, we call it a DHCP Renew, then you will be able to turn the device off when it has more than 3.5 days left, leave it turned off for about 4 days, and the IP will then no longer be reserved.
I hear you ask, Does that mean the IP is lost? The answer is, Only if someone else takes it.
Assuming that once your lease expired, after 7 days from originally being handed out, VM needed to hand a IP to a new device on the network, and yours was the one that had been removed the longest. It would give the new people your IP. So it's possible that you could disconnect your service for weeks, or even months, and still get the same IP when you restart your kit.
Now. As for as your kid goes.
Tell him that it's easy to get someone else's IP, so simply by going online someone can find it. It's also difficult and illegal for people to hack and steal from him so they probably aren't doing it and he shouldn't worry.
You can change your IP with different equipment, but honestly you should just tell your kid that's life. Once we get IPv6 then the block assignments we get will probably be Static, so he should best get used to it now. Also, some services like XBox create a outbound tunnel, so quite a bit of what you do doesn't directly point to your IP.
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I do not work for VM, but I would. It is just a Job.
Most things I say I make up and sometimes it's useful, don't be mean if it's wrong.
I would also make websites for them, because the job never seems to require the website to work.
