the advantage of having young kids is generally they sleep very early which means you can have the early evenings to yourself (assuming they stay asleep).
they also take lots of naps in the afternoon which equals down time for you.
so as a rule, when they sleep you have some free time.
True to a point, but I almost sacrificed my mental health, and I did sacrifice my marriage by not sleeping when the kids are sleeping.
As a single parent, now, I have to go to bed right after the kids do. The unexpected benefit is that I'm much healthier and happier. Also I have several full evenings a week with no kids to use for e.g. learning.
I would stay up very late after the kids were in bed, because I was unwilling to give up on the day. This meant I was never around to help in the mornings, and would routinely sleep in 'till 11 or so on weekends, while my ex-wife got up with the kids at 6 am.
This, coupled with reduced income due to bootstrapping a business created too much relationship damage to recover from.
they also take lots of naps in the afternoon which equals down time for you.
so as a rule, when they sleep you have some free time.