- would you opt for a Wii or Wii U? Can all Wii games by played without any problem? Are there enough Wii U launch titles for kids?
I'd opt for a Wii U if the price is not a big problem to him. As for kid-compatible launch games: New Super Mario Bros. U, Sonic All-Stars Racing transformed, Skylanders, Micky Epic 2 and Nintendoland come to mind, although Micky Epic 2 is said to be a bad port job. Wii games can be played without a problem but you can't play using a GameCube Controller. Seeing as we are talking kids, they most likely don't have GameCube controllers anyway, so that's not a big point.
- can i attach the Wii U to an old crt tv (i read on wiki that the european models do indeed have a scart cable option)
Yes, but you will need to buy a cable for that.
- if the kids want to play together, what sort of controllers do they need. I've been reading that you can't buy a standalone gamepad yet because no games are out yet that support two gamepads. Does that mean that there are no multiplayer games yet or do you have to use gamepad + classic controller in that case.
Buying Wiimote and Nunchuk is a must, not just for multiplayer, but also to access the vast library of the Wii. A Pro Controller can't hurt either for multiplayer purposes.
- worth getting the deluxe set (50 euro more in EU)?
If the kids like to play Nintendoland... yes. Other than that I guess no, because I doubt they'll go digital on their Wii U
- is the gamepad comfortable for small children hands?
Yes.
- i assume you can play on gamepad without television?
If the game supports it.