Vagina muscle control is way more important to me than vagina size. There is an interesting website called the vagina insitute. They have some incredible stats on vagina size from THOUSANDS of women from all across the world.
Seems that the data shows there is very little size difference in the standard deviation from the average.
Like men the majority are very close in size.
As to stretching yes they can, but don't buy into that "babies head" nonsense. When women have babies it takes hours, they scream and yell, they rip and tear, and it isn't pleasant.
True a woman can have a baby pass through her vaginal canal, but only after HOURS of labor, major muscle contractions, lots of screaming and yelling and swearing, and massive amounts of naturally produced hormones to facilitate it.