I would say-depends on climate, geography of what you are located near, and lifestyle.
If I lived near the ocean or that type of climate, we would need half of the space we have now in the midwest and none of the yard because the beach etc would be my backyard. We would also spend much more of our time outside like we do now during the summer time months. We eat outside during the summer etc while the colder time of year, our basment play are gets much more traffic than in the summer when the kids live in our backyard.
We live very close to everything and walking distance to school, town etc. If we lived rurally, we would need much more space for storage of food supples etc.
We have very very cold months and very warm months so we need space for different types of clothing- winter boots, coats etc plus winter playing things like sleds. We also have kiddie pools etc in the back yard area and bikes etc that are not used in Jan with a foot of snow and 20 below temps.
We are not people who save things- we pass them along so someone else can use them and we still were amazed by the amount of "stuff" we had when we moved 2 years ago.