Simply not true. Does your mouth "stretch" and stay big if you have bitten into a big sandwich, altering your appearance and the working order of your mouth? No. Does your anus stretch "out of shape" and stay that way if you are constipated and have a huge poop? NO. Do your nostrils "stretch" if you sneeze a lot or pick them all the time? NO.
Vaginas are similar. They are made to stretch during childbirth and go back to the same size. ALL women have the sides of their vaginas touching while they are at rest. Normal childbirth doesn't ruin vaginal muscles.
All women should probably do PC muscle exercises, to keep good pelvic health. This is whether they have had children or not.
It wouldn't surprise me if women feel like they're different after something like child birth. I obviously will never experience it first hand, but it doesn't seem like the funnest thing to do with a baby.
To answer the question anyway, I haven't been able to tell if my wife isn't as tight after three kids. I'm pretty much just excited to be down there so I don't really do inventory or anything.
I have never been told that I am to loose and I had my son at 17. The doctor that I had said he made me like new maybe even a little tighter. Who knows but I know that I have had men say I am very tight. I do do kegel work outs and that might be some of it as well.
We've all heard that women who give birth aren't as tight as women who haven't...
I have had three children the last was born two years ago. My OBGYN has to use a small size speculum to do my yearly exam. That is a nasty lie meant to make women feel like having too much sex or babies makes them somehow less sexually attractive.
The fact is if you are naturally loose you will be naturally loose after giving birth. There are exercises you can do and products to do the exercises with that will help make those muscles stronger and more reactive. After three years or so the muscles return to their pre-pregnancy condition as does the rest of the body.
It is possible that if a woman has many pregnancies close together she might take longer to return to her pre-pregnancy conditioning.