Parents are subject to the same questions child-free people are about their tardiness and absences. The difference is that, yes, parents have more reasons that this might happen. We can't make our four-year-olds walk to school themselves or walk themselves home from school, let themselves in and boil up some chicken soup. The issue is how employers treat these differences between employees' life styles.
A Canadian federal court upheld a human rights tribunal's finding that employers have an obligation to try to accommodate employee needs as they pertain to childcare. That means if your boss can reasonably let you work the day shift so you can drop your kid at daycare, then she has to. This isn't about every parent trumping every non-parent. It is designed to protect those who would otherwise be forced to leave their job. Having children may be a choice, but taking care of them is not. Juggling work and childcare is hard enough for working parents on a typical schedule.