Being a parent with rules about digital interactions these days is a stressful thing. You're besieged on all sides by the content, other people's opinions about how your kid should interact with it, and the kid's drive to get their hands on any bit of it they can reach.
With tech's primacy in everyone's lives, removing access is a natural choice to use as a consequence for misbehavior – especially once they get past the age where putting them in the corner does you any good. They mess up, you take away access to digital devices. Seems reasonable, especially if you choose a device that's important to the given houseape. I've used it myself to good effect.
But this is where the Devil flies in, on a cloud of stinging, gnat-ty little details. Exactly how do you do that? Take away the device itself? Which device do you take? Do you take the whole device away, or, as a popular meme that's going around suggests, just take away the charger?
I'm not a fan of that these days (even without the gloating bit). Not for some squishy-touchy-feely reason, but because that plan will never last past the first engagement with the enemy. If you've ever played a tower-defense game and think this plan out in that context, you start to see the vulnerabilities in it pretty quickly.
Back in the mists of prehistory when my gang was of an age, I would sometimes revoke their right to play games for a time as a consequence. In order to limit access, I would take out the system's power cord and lock it in the trunk of my car. Or, to avoid pulling apart the entire entertainment center for a one-afternoon grounding, I'd put a tiny padlock in the holes in the end of the power cord so it couldn't be plugged in.
But these days, I wouldn't bother. Plan your defenses. Think about all the different other ways they can get the charge they need. What cracks can they slip through to circumvent your strictures?
Let's go through a scenario from today's world. You've decided to get your kid off their phone for a week, and to make it so you're not also taking away their alarm clock and everything else, you just take the power cord. It is possible they will simply accept the punishment, but if they don't, you're going to have to defend your decision against their wiles.
For starters, are you going to schedule this out into the weeks/months range? These devices often last quite a while on a single charge these days. It's not going to die in an hour. My phone lasts two days, and that's with my insane data usage for work. A full day is pretty standard on devices, unless you're playing Pokemon Go. If they're careful about how much they use their data plan and put it in airplane mode when they're not actually using it, they can last longer than I bet you realize.
First thing to think about is power itself. With modern devices, outside of some really weird outliers, it's only important that the ends of the cord fits. Even if the device requires a fiddly voltage, the hardware is generally equipped to step normal household current down to something it can cope with. It's part of the USB Standard for power delivery. So they can use just about any outlet, anywhere, to get juice from. The trick is going to be plugging it in.
Most devices (particularly newer ones) use a standard connector plug for the end that goes into the device, called a USB Micro connection. If you're in Europe, it's established that way by law. Older devices may use a USB Mini connection (it's the fatter version of the Micro).
You can get cords with those connectors on just about everything out there. My grandson has a Hot Wheels race set that comes with a USB A to Micro charging cord for the cars, and so does his LeapPad. Look all over the house. Sibling's devices will have charging cables. I have a mixer in my kitchen that uses an Edison to USB Micro charger. So does my portable sewing machine, and one of my power screwdrivers.
Do you have a car charger for your phone? Bet it'll work. And some cars don't have to be running. All the kid has to do is set their phone up in the car and leave it for a while. If they retrieve it before you get in the car, you won't even know. A 12v car battery barely notices charging a tiny cell phone/DS battery.
The other end of whatever cord they got a hold of also matters. Even if their device requires some odd proprietary hookup into it's own gullet, if they can get a cord with that correct end and the other end is USB A (the connector used on a thumb drive) then they are really free.
Computers (both desktop and laptop) are people's first thought, but you can get USB A ports on just about anything. My living room television has USB ports in the back to allow for firmware updates/service. So does their Xbox/Playstation/Wii. Many power strips come with integrated USB ports these days.
If you managed to not have any of those around, all they need is a USB to Edison converter (like the brick at the end of a Mac charger). Plug it into any outlet anywhere in the house and they're good to go.
If you think those are hard to find or expensive for a kid, think again. They don't have to go to an electronics or game store. My grocery store has them over by the batteries. Your local Walgreens has a great selection. Look over where they also buy those earbud headphones that are the electronic equivalent of sticking their fingers in their ears so they don't have to hear you.
Oh, and speaking of batteries, did you know one of those cute little auxiliary battery packs for devices costs about 10 dollars these days? I picked mine up at Marshall's and it has a USB A port, so it will provide power to just about anything (see notes above about cords).
Oh wait, what about their friends? Their friends, to whom they go for commiseration about their fascist parents, know these things and probably have what they need. If you missed that, then the only thing you're actually in charge of is Fantasy Land.
So ground them! But that won't do it, either.
Are you going to keep them from school? Their friends probably have a charger in their purse/backpack they can plug things into while they're sitting in a class. They don't even have to match types of devices. The brick from the end of an iPhone will happily charge any other device – the cord just needs a USB A connection. The school day abounds with opportunities. Not to mention after school – dance or music lessons, tutor sessions, sports practices, church activities, etc. You're not going to be able to keep them from plugging it in behind your back somewhere. It may not be the best charge ever, but it will work in a pinch. And they can milk whatever charge they have for quite a while.
My motto is the only way to win that kind of battle is not to have it. There is no way to defend a tower built on sand, with all those weak points. If you don't want them on it, then take the thing away, cord and all.
Of course, that just defers the battle. Now you have to keep the whole thing away from them, and worry about all the other things they might find while searching.