How do you know? My friends who did have kids had intricate dynamics around that where 'want to have' was not really a big part of the equation. Pressure, religion, 'that is what you do', 'my spouse wants to', 'maybe now life gets better' etc are often part of the equation. For the 'want to have' you will need to look inside people's heads.
"More than nine in 10 adults say they already have children, are planning to have children, or wish that they had had children." [1]
Is it possible that most respondents were lying? Yes. Probable? No, especially given that humans are biologically wired to want children.
1. http://www.gallup.com/poll/164618/desire-children-norm.aspx
After all, all the people who didn't want kids, and had a choice about the matter died childless and never passed on their anti-replication genes.
15% of women ages 40-44 in the USA have never given birth, from which we can pull 85% of women ages 40-44 have given birth, as of 2014.