I have run into this situation frequently this year. One parent in particular is troublesome about this. When I call home for a feverish or sick child or if the child has lice, the parent just says "I can't pick them up. I don't have a car". She was quite nasty about it when this last happened. The child/children end up staying in the front office or in my clinic all day, and we end up sending home on the bus despite the fact that it's against school policy to do so. This has happened several times this year with this parent. The principal doesn't want to make any waves with parents, so she goes along with it. I think in this case, Mom knows we don't do anything about it so it's of no consequence to her.
What do you do at your school? I'm getting tired of being a free babysitter....