So I've seen in a previous job where someone was complaining that a guy was leaving at 4pm to get his kid and how it was unfair just because he had a child.
What that person bitching and moaning didn't see was that the parent was getting into work MUCH earlier than him, and would regularly log back on when getting home.
Sure there are some parents who take the piss, but there are also plenty of parents that put the hours in and more, they just need a little flexibility because childcare and the associated costs are a fucking joke and society isn't set up to enable single income families.