It's one of the reasons why "date night" was invented.
It's also been estimated it takes nearly $300k to raise an infant to adulthood in the U.S. Naturally the more children one has the odds increase there will be financial stress and sacrifices. This assumes the kids don't have any "special needs" or turn out to be "hellions" causing havoc to society! Otherwise it's worse!
Just keeping up with their schooling and after school activities while dealing with unpredictable challenges as they learn via trial and error can cause stress and worried nights.
Also it goes without saying the more people you have in your life that you love the more people you have to be concerned about their welfare and how life and other people treat them.
I know people with "adult children" who find themselves stressing in their "golden years" raising grand-children!
Child free doesn't mean "stress free" but it does mean one usually has far less stress in their life than those with children.