You can only figure out which baby is in the baby photos by reference to clues in the background.
When you realise that the last two babies have exactly 7 baby photos between them, whereas the first three have many boxes apiece.
When then youngest two answer to an amalgam of their two names.
When you realise the youngest four did all their afternoon napping in their carseats while someone older was being schlepped to whatever class you thought was so important at the time.
When you give up on separate colours and styles of socks and knickers and invoke the rule 'first up best dressed' (from the permanent laundry basket in the kitchen of course).
When they spend time together negotiating the daily shower schedule for the coming week. And there is never a nice, dry towel in the bathroom. (Oh the joy of a houseful of teenage girls plus DS who never stops complaining rightfully that his razors are all blunt and full of hair.)
Some of their fondest childhood memories involve being deposited outside in the cold American midwest winter while they tried to remember what it was that was so important they had to try to scream the house down about it.
When all the downstairs floorspace is instantly covered with bags, shoes, hats and jackets when they get home from school.
When they get through the better part of a whole sliced loaf making lunch for themselves every day.
When three or four more in your house makes no difference, and when you think it's awfully quiet when one is away but you still have way more than the average number of children underfoot.
When you get really, really good at packing for holidays because the alternative is to rent a truck, but you still manage to look like a family heading off on the Oregon Trail when you attempt to go to the zoo, and when you get there you spend your whole day counting one-two-three-four-[panic]five. But you only go to the zoo (or anywhere else) on free days when attractions are jammed so the constant headcount is very necessary. And when the thought of taking them all to the beach brings you out in hives.
You know far too many songs learned from watching children's TV and films over the years and you can recite Beatrix Potter books from memory if someone starts you off.
When you realise that your youngest child's friends are all only children and you wonder what she is trying to tell you.