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.
There is a lot of research on this topic. I know later studies contradict earlier studies, but I'm not sure who to believe here. Wondering if anyone can help.
In case it isn't clear, the basic question is the effect of having children on happiness.