I've a friend who was number 3 (I think) of 6. He and number 1 were boys, the rest girls. I'm not sure of the exact ages, but I know the youngest is quite a bit younger than the others. He said they LOVED it as kids, but looking back now, he realises there were a lot of negatives and he wouldn't have a big family himself.
He says they basically formed a big "gang" and didn't really have friends outside the family. He never went to friends' houses or had friends round to his house, and he says he grew up not really knowing that there were other ways of doing things in life.
His brother moved to New Zealand fairly soon after graduating, but the rest have all stayed near their parents. His sisters do everything together, see each other most days etc. Their kids are basically brought up as siblings rather than cousins. They've all struggled a bit to maintain healthy relationships as adults - several divorces quite young, a couple of affairs etc. None have large families themselves (biggest is 3, but the younger 2 are twins).
If you asked them, he says his sisters would say their childhood was great and they're all really close, but he thinks there was a lot of pressure to maintain the illusion of a "big, close family" and that's not the reality. He says he always felt like a number (in fact, his sisters all have matching tattoos which indicate their birth order or something- he described it and we were all a bit freaked out, it sounded slightly creepy), they were all expected to think in similar ways (there are family portraits in which they're all dressed identically) and generally it wasn't all that healthy.
It's probably largely to do with his parents, obviously, rather than specifically because they were a big family, but it does always make me wonder when I hear someone say "our huge family is really close" whether they've been trained up to say that rather than it being the reality.