This is brilliant.
"When you don't have children - as I don't, thus far - one entertaining thing to do with friends who do is as follows. Wait until they're gazing, lovestruck, into the eyes of their newborn baby, tucking their toddler into bed or proudly watching their 21-year-old graduate. Then creep up behind them, slap down a copy of the Journal Of Marriage And Family, vol 65, no 3, and triumphantly declare: "Ha! You may think parenthood has changed your life for the better, but, in fact, the statistical analyses contained herein, along with numerous other studies, demonstrate conclusively that having children makes people, on average, slightly less happy than before!" Then walk away cackling. They may never speak to you again, but that won't matter: you will have won the argument, using Science."