Not all of the joy, but a lot of it. My dad was born in a village in Bangladesh. Like a real village. They practiced subsistence agriculture and didn’t get electricity until the 1990s. One out of every three children died before age 5. They lacked of everything a typical child-free American would need to consider life tolerable. But believe it or not, most were pretty happy.

As of 2016, the average income in Bangladesh was around $2/day: https://www.ceicdata.com/en/indicator/bangladesh/annual-hous....

The same year, 66% of people reported they were “very happy” with their life. https://www.thedailystar.net/frontpage/bangladesh-tops-list-.... Sure, Bangladeshis aren’t as happy as Americans. But the average Bangladeshi lives an existence that would drive your typical child-free American to suicidal despair. What do they have?

That's not really supportive of the idea that most joy comes from kids, or that a society without many would be joyless.

I'm not contesting that children can bring joy. I am contesting that they are the only source.