I'd say every single thing one does in a day is 2-10x as difficult and 2-10x as time-consuming (usually some amount of both, but the two don't always scale in p

I'd say every single thing one does in a day is 2-10x as difficult and 2-10x as time-consuming (usually some amount of both, but the two don't always scale in propotion) when youngish kids are involved. Things that might be quick & mindless become slow and mentally taxing, that sort of thing. Of course making mistakes in raising kids, or simply getting unlucky and having kids who are sick a lot or whatever, makes things even worse—in the best case everything's still much harder and takes longer. And each extra kid bumps up the difficulty & time factors to some degree.