Most kids will always compare something. I have one DC who used to be very concerned about the size of our house vs. friends' and one who doesn't care at all. We make a point to talk about what we love about our house and our neighborhood. It seems to have mattered less as he got older, and was exposed to more friends with both smaller and bigger homes.
Personally, I prefer a smaller home and wouldn't want a really large one, both from cost/maintenance and family interaction. Still, there are times when I wish the living room were bigger or we had a mudroom.

In those time, browsing Apartment Therapy is helpful -- I get ideas for tweaks we could make and my house seems quite big compared to most of those highlighted on the site.