This is a completely first world prob, and I only mention it here because some of you reading this may get the privilege of designing and building a house.
My husband and I did just that back in 1996-97.
And we purposely built a large basement that was a total kid's space. On the days when I thought I might spin out of control, I would say, "Ok. Everybody to the basement, and don't come up until I tell you." It was/is an amazing space. I know my children have many happy memories playing in it.
However, the caution I'd like to issue here concerns just how isolated that space is when...your son wants to go hang out down there with his girlfriend. Or, that sweet little daughter of yours takes her boyfriend down there.
They are going to play pingpong.
Then, they are going to watch a movie.
At night. Late at night.
That's a lot of alone time, so my husband and I would play Rock, Paper, Scissors for whose turn it was to just casually sashay through the basement like that's what we did every night.
We were thinking, "Here we are again just making the rounds to make sure...uh...to make sure...uh..." but what came out was, "How's the movie?"
So, so awkward.
But we did it. Probably not enough, but we did it.
Anyway, I say all that to say, if possible, in a perfect world where money is no object, build a basement for when the kids are little. Then, when they become teenagers and start dating, destroy the isolated basement and build a room right off your family room.
And make sure the wall between it and the family room is made of glass.