Fine. A strictly capitalist take on the situation: your inability to negotiate for desirable hours & wages is not the responsibility of anybody but yourself. Go work in a union if you want everybody to have the same contract.
This all comes back to the fact that everyone should be protective of their time. I’m single but regularly run errands, exercise, go grocery shopping etc in the “middle of the workday”. I get my work done. Nobody complains.
It’s just a matter of knowing and recognizing your own value.
Parents needing such negotiations may be a "hidden cost" that y'all aren't considering. Also, parenting is a ton of work so when I kick off the paid job, I'm still working 'til 9 most nights.
Out of curiosity, was there ever any situation that your manager would reach out and ask for you to put additional time because of an urgent requirement / situation?