I don't have a citation but I have eyes and I see how real parents in my life have gotten by. Besides, even if it is somehow more work than 3 hours per day, it is probably close to that amount and far more enjoyable than most jobs. If you count sitting around watching your own kids play as "work" that demands "compensation", I feel bad for you.
Wait, do you have kids yourself? Childcare days with my 2yo are much more draining than most work days. It's never a case of just sitting and watching.
As a parent, I believe I speak for many when I say [citation needed].