Another possibility is that people tend to have kids 1-3 years after getting married and the happiness bump we’re seeing is mostly that people really like the first few years of marriage. Not sure how to interpret the (differently shaped) happiness bumps in the “unmarried” case, though.
I’m tempted to send the “with controls” graphs to the newspaper and suggest the headline: HAPPINESS CAUSES CHILDREN.
That’s not that strange, if you think about it.
Another possibility is that people tend to have kids 1-3 years after getting married and the happiness bump we’re seeing is mostly that people really like the first few years of marriage. Not sure how to interpret the (differently shaped) happiness bumps in the “unmarried” case, though.