How to do a "family home computer" these days?

You should put a coin-operated claw arm and a bunch of mini rubber ducks in that.
Originally I was going to be teaching one of the kids I volunteer with how to build a computer and was going to go all out with custom water cooling. That didn't work out so I went with air cooling. Still that damned video card takes up a crapload of space...thing has to weigh close to 10 pounds