Earlier quoted context omitted.
The problem is, people without children are told (or required) to pick up the workload left behind when the coworkers having children taking (multiple) weeks off. For once or twice that might be okay, but if became a chronic problem, no wonder they are not happy.
Yes, they should be unhappy about that: at their managers. Not at their colleagues attempting to care for children during a pandemic. I've heard a related thing about US workers resenting colleagues for taking paid time off for similar reasons, and it's just as weird to my European eyes. The difference a decent labour movement (or the legacy of one) can make to industrial relations is stark
If you give a tax rebate to anyone who's last name starts with A, are the other people not allowed to be annoyed, given that they have to pay more taxes to make up for the rebate?
"Why can't you just be happy for the A people?" feels weird.
Just pay those not taking time off for the time they would've taken off. It's not a complicated concept, it shows appreciation for them working harder than they'd need to if their colleagues were around.