We have four, which doesn't seem big to us because we are in the midst, sort of like having our noses stuck against the painting; it's hard to tell the actually scope.

Ours are still very young and having witnessed the interactions of children in families with one or two children, there are definitely some qualitative differences. I don't know how much is attributable to family size, parenting, personality, and of course the overall dynamic of the people in my particular family- and I'm not sure how anyone could determine this.
So, with that caveat, I'll share what I've noticed.
In our family, there is very little sibling 'rivalry.' It happens, but it is not insidious or an underlying relational aspect of the children's lives. When it happens, it's overt and has a beginning and an end, as in,
"I want to show mummie first!"
"NO! I want to show mummie first!"
"NOOO!!! IIIIIII want to show mummy first!!!"
Then maybe a scuffle, and then once the 'showing' is done, the rivalry stops.
With my brother and I growing up, the rivalry was our manner of relation when in the presence or anticipation of our parents. I have seen this to be fairly common with families with two children, although my own upbringing was a very neglectful one and I don't know to what extent actually nurturing each child would alleviate the underlying desperation for attention. Maybe mums with two can give more insight into this dynamic in a healthy home.
I do not have nearly as much involvement in their play (than the mums I've seen with one or two) and they are years ahead of their age-peers in social development, showing maturity and empathy expected of children twice their ages. I often think that social milestones are determined according to small families because I cannot fathom how a child with many siblings could even survive without developing empathy, negotiating skills, non-violent responses, etc... in tandem with learning self-feeding and object manipulation.
These are such natural developments in a big family; nobody here is directly 'taught' empathy or even manners because it becomes exceedingly obvious to each child what the accepted social expectations are when they are reinforced exponentially each day with so many people.
My friend wanted to teach my children manners the other day because she's teaching her daycare children during their 'manners time' (I don't know why she likes to experiment with my children...


. I was perplexed and told her that our children figure out before they even speak that kind speech is preferable to demanding and that the words associated with manners come pretty naturally when they are a normal part of our language- not separated as 'manners words.'

Obviously there is some differing parental philosophy here, but my own ideas about much of what I thought would be a normal part of mothering have been changed by the very different dynamic in having four as opposed to one or two children- where teaching certain things that we don't may actually be necessary. I hadn't accounted for how much they would teach one another, or how much learning would happen as a result of just being as many as we are, for instance.
Two of our boys were taught by their brothers how to use the toilet (or squatty potty as it is for us), and they teach one another all day, delighting in the opportunities to share what they know and can do with one another.
It is not like having two children, doubled in chores and work. It is completely different, imo.
It is also very loud at our house. There is constant chatter and the sound of feet hitting the floor. It's summer though and in winter, they hole up with us and spend copious amounts of time with books and drawing, so there are long periods of relative quiet during that time. Spring and summer are much livelier in that sense than at any one else's house (who has fewer children, that is).
Mostly each new baby has brought something with him to us and made a new dynamic emerge from the relationships we've developed with them. I thought that when we had new babies, they would sort of be incorporated into the whole, but that hasn't been the case at all. Each one has indelibly
changed the whole and in wonderful ways we couldn't have anticipated before they came.
By FAR the majority of difficulty I have experienced as a mother has been due to a lack of support for
me.

I would not find my days nearly as taxing if I had a reliable break and time for work that I find personally meaningful in self-expression (aside from mothering), which is something that after six years is finally coming together.

I have not required for myself what I have assured for everyone else in my family and it has taken this long and my extreme poor health (now recovering very well) to convince my dh of my need. In any case, he now gets it and he is my only source of support. The other thing I hadn't anticipated was how quickly we were dropped by friends and family at each successive pg announcement according to their level of tolerance. That was sincerely shocking.
Overall, though, this experience has taught me more about myself and others than I would have guessed and I have become a much stronger woman than I ever was before, even while my physical weakness plagued me for years after my c/s's.
Many people say to me that they couldn't do what we're doing- having four children- but we couldn't do anything else. My dh used to say after each baby that he couldn't imagine having X children, and I remind him that before he had 1,2,3, and 4, he couldn't imagine that either. There's nothing to plan in a way. Once you're doing it, you're doing it. I answer the question "how do you do it?" with "I just do." I don't know how. How do you love one person? How do you love ten? You make a choice and act on it. I can't think of anything simpler- or more complex in its simplicity!

I think it takes or induces a level of strength and confidence to live as we do that I wouldn't have had it not been required of me in having many children. In many ways, we are like the old pioneers- going it all alone, as a family. In other ways, others benefit immensely from their interactions with our children and in seeing our family in action, others who were previously baffled by the desire for children or many children, have changed their attitudes about it (several families who were unreceptive to the idea of having more than two, having seen how four functions, have now decided to try for four children themselves). Anyone who sees us personally doesn't ask how we do it; we're like a school of fish, all swimming in cooperation around and with one another in a mostly graceful way, not hindering, but allowing for the progress and growth of one another while still moving forward ourselves.
I wrote on the trampoline safety thread about how our boys are so accustomed to being together and moving around and with one another that four of them can be jumping and tumbling on the trampoline without any incident. They are like a circus act

, or a dance troupe. They move as though they are extensions of one another and anticipate one another fluidly.
I always make a note when in this sort of discussion that my children are not particularly 'easy' or 'compliant.' At least three of the four have strong tendencies toward ADD I just say they have it because it is so obvious) while being advanced in every usually measured cognitive, social, physical and intellectual area of development.
Being that both dh and I have ADD as well, we function with presuppositions that many others do not have and that influences the ease of our functioning as a family. If we tried to fit a 'mold', we would all wilt. Key to our health has been to work with the
actual dynamic we have rather than what might be expected of us, like a structured life of any sort. Home-based learning is essential to us as is a very fluid un-schedule to our days. Rigidity doesn't serve any of us and so we make allowances for when that might be imposed and plan to incorporate the rigid thing into a fluid day without being constrained to it (appointments for instance).
I thought I should include that because however we function and for whatever reason our family life is healthy, our particular way of finding solutions for our particular needs is pre-eminant.

That said, if you want to have three or four or ten (I'm assuming since I only have four) children, you'll figure out what to do when it's time. I don;t know how else anyone could.