I think it depends on how many children you have and what career. Four children and jobs with loads of travel will be hard!
I've been a single parent and I think that's actually helped in a way. (Hear me out!)
Employers have known that I can't get to work early or leave late, and that's been non-negotiable. But I work hard when I'm there, I'm ruthlessly organised at work and I get shit done. I used to spend my evenings studying for my professional exams when my son was in bed. I've done a law degree part time as well, again, studying in the evenings whilst working FT.
This would have been twice as hard with two children, and probably with another adult to worry about too. If I wanted toast for dinner to save on time, that was fine. I didn't have to make conversation with a partner in the evenings or do double the washing or clean up anyone else's mess.
Yes, there were times, particularly in the first year of nursery, when I thought I would crack from the stress and all the sick days and I think every single one of my 25 days' leave were used to cover his illness rather than anything fun.
But now, years on, I'm doing well professionally and I think I do have it all. I'm strict about overtime, I don't stay late for the sake of being seen, but I'm damn good at my job and I'm paid very well. I also like to think I'm a good Mum most of the time!