It depends on whether the state defines that as a "school bus" or not.
School buses are often exempt (although for kids under a certain age or weight, may not be.) However, the definition of school bus varies from state to state, and may also depend on whether the daycare operating the bus/van is operated by a non-profit organization or not.
However, they are professional care givers. They should be held to a higher standard of care, IMO. That should include best practice in transporting children. I'd suggest you give them information on best practice and see where it goes from there.