It's an odd phenomenon, but in certain situations total stranger feel they can accost you and ask questions that when properly considered are at the very least impertinent and more likely downright rude.
For some reason, when a couple has more than three children, and occasionally more than two, people they have never met think it is perfectly reasonable to ask whether or not the couple plans to have more children. If one considers this question, it is really asking about the couple's birth control choices and decisions. That is not generally a topic I would discuss with most of my friends and certainly not one with which I chat up the parking garage attendants.
And yet, if a couple has several children, society thinks its okay to ask, "Are you done yet?"
Oddly enough, I am not asked these questions when my children are out in public and acting their worst, but rather when they are at their best. Maybe it is simply out of fear of the terrible howling masses that cling to my pants legs that I am not approached and offered advice and free condom samples when my children are at their worst, but I always wonder why in those times when they act like angels, I frequently ellicit pitying looks and questions that make me think the asker doubts my sanity or ability to control my lustful urges. In their minds, even when children are perfect, four of them is simply too many for any one.
I never mind the comments that I have my hands full -- because I do have my hands full. I like it better when the comment comes from someone opening the door or carrying my groceries than from someone merely observing, but I can tolerate it either way. I like much less questions that are really comments about when my husband and I should cut off the kiddie production. Whether or not I want any more is really not their business, but when I, on occasion, suggest that we're hoping to have at least a few more (which I can't actually say is an accurate statement) the jaw drop that always follows is worth it.
It's rude to ask if I use birth control. It's rude to ask if I'm done having children. If you're going to follow the question of, "Are you planning on more?" with, "I have a dozen and large families are wonderful." I might forgive the rudeness. Otherwise, keep the question to yourself.