One of the first things people say when the number of children I have is brought up is, “Wow, you must be busy, how do you do that? I have trouble with my two.” My usual response is “Oh they entertain each other it isn’t so bad.” This is usually met with a dubious look, the eyebrow cocking up a bit to express a bit of doubt.
But it is true. Though it is hard to explain in the short span of a quick conversation. There is something that I dubbed “The Sibling Effect” that comes into play when you have a larger family.

Basically, the sibling effect is a result of each child being somewhat less the “center of the universe” and slightly more part of “team Family” than the normal American child. Mom and Dad switch from being the people in charge of giving the child everything they want to “the bosses” and siblings are less competition for family resources and more fellow team members.
The Changes: My first two children are 18 months apart. When Rachel was born Ashley was excited to be the Big Sister – she would fetch diapers and hold things and watch the baby. This went on right up to the point that baby sister started getting into her stuff, then baby wasn’t as much fun, in fact she was down right annoying.
By the time Christopher came around Ashley had more or less gotten over the fact that little siblings will get into your stuff. This baby wasn’t quite as exciting as the first new sibling, but being helpful when you are 7 is still a thrill. Plus Ashley was now old enough to hold the baby, make the baby laugh and understand more of what was involved. There was also a fellow “victim” with the annoying aspects of older sibling life.
I suspect four children will definitely create the sibling effect and maybe three depending on the parenting style and how close in age the children are, but once the dynamic is created it changes the parent/child dynamic and creates a very different sense of family.
Among our community of larger, homeschooling, Catholic families one of the things I notice most is how open the older children in the group are to watching out for the younger ones – not just their siblings, but all the children in the group.