Hello,
if you are already installing/having installed LAN cabling (there are people who swear by WLAN - I am more a fan of cables as long as it is about connecting immovable devices), you should plan generously right away or at least lay corresponding empty conduits.
One socket in the children's room in some corner would not be enough for me - if you rearrange the room, you suddenly have to run a cable across the room. So my suggestion would be at least a double socket in 2 corners each. In the study maybe even more, e.g. if you have a network printer that should also be used from their computers. Or to connect a backup system. And in the living room also at the places where potentially the television and hi-fi system are located at least double sockets. My TV already has a network connection, the Playstation too, in the future there will be more TV over the internet and the hi-fi system or the iPod also need a connection. And possibly you need one or two places in the house where you can connect a WLAN router to have good reception throughout the house and maybe also in the garden...
The patch panel and the network switch don't necessarily have to be huge - you don't really use all sockets simultaneously, so you only need as many connections as you actually use. And the devices are getting cheaper all the time, so you can retrofit later. With the cabling, it becomes awkward if you have to get at it again.
Oh yes, you can also use a Cat7 cable already laid for connecting a telephone - the corresponding cable just has to be patched not to the network switch or router at the patch panel but to the telephone system. So that should also be considered.
About the technology: The number behind Cat says something about the maximum possible transmission rate of the cables and sockets. Cat7 is currently, I think, the fastest (10 Gigabit), but there are hardly any Cat7 sockets. Cat6 is still good for 1 Gigabit - if more is needed, the sockets can be replaced later. Currently, 10 Gigabit switches are still very expensive and with 1 Gigabit you currently have enough bandwidth. Price-wise, Cat7 cable is not much more expensive than Cat6 - so in my opinion, it makes sense to lay Cat7 right away.
Best regards,
Jens