I agree in principle, and do sometimes get mildly annoyed having to cover for people because they are out due to parental obligations, but overall I really don’t mind or care that much. I’ve had to do it a number of times now and sometimes it can be very stressful but that’s why I get paid. Being a parent sucks so I feel bad for them having to put up with all the bullshit, it’s not like they are off having fun when they can’t be at work because their kid is shitting uncontrollably with a high fever or whatever nightmare is going on. Not having kids is great, the occasional extra work or responsibilities that comes with being more reliable than coworkers with kids is the tiniest of tradeoffs for me. Maybe it helps that I like my coworkers and am happy they get to be responsible parents. Additionally, if your boss or someone higher up is out on extended parental leave it can be beneficial to your career if you fill in for them and get some time working “above your station” because your org gets forced into it. I know it was for me early in my career.