For members of my parents' generation, 5 kids was probably the median for a typical LDS family -- lots had 7 or 8, some had 3 or 4. But 3 was definitely on the low end. 2 was almost unheard of for a devout LDS family. Now, the norm is probably 3, with plenty at 4 or 5 and also plenty at 2 and even 1. It's relatively rare for even a devout LDS family with parents under the age of 40 to have more than 5 kids now.
In other words, women nowadays are making the decision to have fewer kids, which opens up lots of possibilities for them. A woman stay home for 8 years or so until the kids are all in school and then go to work. That wasn't nearly as possible 30 years ago, when women had 5-7 kids, and thus wouldn't have all their kids in school until they were in their mid-40s.