The experience of having kids involves a relationship that spans something more than 25 years. I remember seeing research done on people that have had the full experience and the overall ratings of happiness were lower.
Citation needed
Many Parents Are Happier Than Non-Parents — But Not in the U.S. https://time.com/collection/guide-to-happiness/4370344/paren...
Having kids makes you happier, but only when they move out https://www.newscientist.com/article/2213655-having-kids-mak...
The depressing reason why having kids doesn’t actually make you happier https://www.marketwatch.com/story/one-theory-on-why-having-k...