Before the pandemic, this resentment already existed. It's just exacerbated now. There have always been hidden benefits for people with kids. And although those benefits don't nearly make up for the extra responsibilities of having kids, those without kids feel that it's unfair.

For example, someone with kids gets a bigger insurance benefit. Usually managers are pretty forgiving when someone says they need to leave the office at exactly 6pm every day to get to soccer practice, leaving the single people stuck without the same excuse. Oftentimes the single people are asked to do the extra off-hours work "because you have no kids so you don't mind right?"

This is just an extension of that, which is perceived as unfair to the single folks.