This law is only for grades 7-12, so most affected kids can get themselves to school, or don't need direct supervision between when parents leave for work and when the bus arrives.
I'd also point out I've never lived in a school district that started elementary school before 8a, so these parents must have had solutions for those years. The real problem is going to be if elementary schools get pushed forward to start at 7a and release at 1p or something crazy like that, but I know most districts don't want the liability of 8 year olds waiting for the bus in the dark along side a major road.
My 7 and 9yo kids start school at 8:50am, and don't get off the bus until 4:30pm. It's ridiculous. They're young and need time off but because the district moved everyone back to make room for the High Schools now elementary kids aren't home until half past 4.
Not enough time for them to play in the afternoons now.