Nattavudh Powdthavee tries to reconcile studies that suggest children don't make parents happier on balance with our shared belief that they do:

...we tend to believe that the rare but meaningful experiences – such as seeing our children smile for the first time or graduating from university or getting married – would give us massive increases in our happiness. And indeed they do, but these boosts in well-being, often to our surprise, tend not to last for very long.

One explanation for this lies in the nature of these experiences. How often do we think about these rare but meaningful experiences on a day-to-day basis, that is, if we are not prompted to think about them? It is, if you like, like winning a lottery. We may be incredibly happy at first if we win £1,000,000 from the National Lottery. But soon enough that money will go into our bank account or into our other extravagant spending sprees in the forms of nice cars or a big house in the country, most of which, after having got them, we do not spend a lot of time thinking about everyday (see, for example, Kahneman et al., 2006). However, because the experience of winning the lottery is so salient to us – perhaps partly because it is such a rare event – if we are asked to think about it again, we are likely to exaggerate the value that it brings.

(hat tip: Vaughan)