I looked into this a couple years ago and wrote up what I found:
Summary: the research isn’t that good, is all correlational, and how parenting affects your happiness varies widely by demographics (age, gender, income). Neither a simple “parenting makes people happy” nor a “parenting makes people miserable” are justified.
I looked into this a couple years ago and wrote up what I found:
http://lesswrong.com/lw/erj/parenting_and_happiness/