How about if some parents or maid can accompany the kids in the school bus? Of course, they pay and occupy one more seat. They can help looking after their kid and bus driver will not be too bad in driving as they are observed. Bus school company may not like of course. Parents should insist or raise this option to school.
My elder girl started taking school bus when she was 2 years old. That was the school's private school bus & also had teacher in the van.
My smaller girl will start taking school bus next year too (2 years old). They are not going to the same school so it is outside school bus but I cannot do anything because we all need to work and the maid has to take care of two kids - no time to bring my girls to school (two different schools)
so far ok. My kid started taking school bus in Nursery. However, I did bring him to school for the first 2 months so that he doesn't have to adapt to so many new things (new school + school bus) at a time.
As long as you have checked if they have seat belt .. then ok