My family is considered "underhoused" by the US government, because we have fewer bedrooms than occupants. I certainly don't feel it myself. We have three bedrooms for the four of us, and even chose to use the third as a media room until the kids get sick of the bunk beds.
We've lived in both sorts of situations in the recent past. Extra rooms give you flexibility and the opportunity for privacy, which is really nice with young children who aren't sleeping well yet, and might disturb their siblings if they were bunked. There are trade-offs involved in both situations, which one is better for you just depends on what you value.
I generally think that there's too much of a slant toward large houses in the new housing stock in the US, though - they're more expensive to buy and maintain, and generally not the best choice for young people.
