Why'd the mom drive her kids to the bus stop??

A bus stop typically some place that is close to the house, so that they kids could walk there. We can see this the day that school gets cancelled and Donnie just walks home. The reason she drives them to the bus stop that particular morning is because they weren't home, they stayed at a hotel that night.

We don't really know the geography of the town, but we can assume the school is far enough away, or in a different direction for it to not be worth it for her to drive them the entire way.