Cable is relatively cheap. It doesn't need to be finished off at this point in your project, so as long as you have a backbox in place at the various outlet points then there's nothing to stop you fitting a 2 gang blanking plate for now until you've a more certain idea of what you actually need to be live.
I'm not entirely convinced that kids are using TV in the way that we adults do. Theirs is an online world. The figures from Ofcom confirm that the device of choice for watching "TV" is a tablet followed by a smart phone. Linear TV viewing hours are falling. Kids are more likely to reach for the tablet and the streaming app than the TV remote. They'll still use a TV for playing console games though. Consoles also provide streaming services (Netflix), Youtube, some social media and messaging. They're not plugging in laptops or even NUCs, as far as I can tell. They're more likely to cast from a tablet or phone to a local TV if they want to watch on a bigger screen.
The way I plan structured wiring is to put a couple of network cables to a low level point where most of the power sockets live. I'll place one higher up where a TV is likely to live. You'll put a spur up for power (double socket), but try to keep power cables at least 10" away from signal cables if they're running parallel with each other. I'll also put in good quality coax (Webro WF100). That might sound odd given what I said about kids and their habits, but coax remains a high-bandwidth connection format and it's useful for Freeview, Freesat and Virgin Media*
Now for the future-proofy bit..... Other than 4K HDMI cables which is a "now" technology, and the increasing reliance on the internet as a video source, we really don't know what the next set of connectors might be for AV in the future. 8K is very likely to be on the cards at some point in the next decade, and HDMI will need a major rework if it's going to continue as the domestic connector. Chances are a version of DisplayPort will take over. But these are connections from a source device to a display; some kind of internet- or satellite- connected media box that then plugs in to a TV. The point is that there'll be an umbilical running up inside the wall. If you want to stay ahead of the game it's not about guessing which cable to install. It's about putting in the trunking so that you're ready to change cables easily. Bury some mini trunking big enough that you could pull a couple of HDMI cables through it while there's already some cable in there.
Also provision for a soundbar. TV audio doesn't look likely to improve. This is why you fitted a 2G spur rather than a single gang.
TVs will continue to be internet connected, and the apps on TVs will continue to run with a tonne of bloatware and be poorly supported beyond 3 years, so be ready with a secondary source. We come back to consoles again but also Chromecast, Firestick and Android boxes.
So, quick recap - TV point is power (2G) and 1 Ethernet + 1 coax plus the top end of a conduit that runs inside the wall for (currently) HDMI. The sound bar takes power from the 2G socket. Audio signal will be from Optical or HDMI ARC.
At low level you have at least 2x Ethernet unless you plan to run HDMI over Cat/HDBase-T extenders. In that case you could do with three. Anything in room that needs multiple Ethernet connections can be served with a local switch.
Oh, nearly forgot. In the comms room don't bother putting wall-mounted Ethernet sockets. It's a waste of time and money. Bring all your tails back to a 24 port/48 port Ethernet patch panel. You'll punch-down the cables to the ports.
Label everything. Test everything.
* Strictly speaking WF100 TV/Satellite coax isn't up to par for VM. Their requirement is a triple shielded coax called HD100. However, since VM are economising and running with an aluminium/Mylar shielded cable now then it seems like they're not quite as hot for technical superiority.
