No they won’t have car seats, you’d have to provide your own. If they were going on a motorway jd personally be taking my own child.
The driver will have undergone an additional assessment and there will be risk assessments in place. The minibus itself will be regularly serviced and well maintained. They will have the same seatbelt as you'd find in a car. As for avoiding bad roads, that will depend on many factors- where they are going, time of day and journey time. If you're concerned speak to the school. (I'm a teacher).
They won’t have car seats. My son used to get sen transport to school on a mini bus and that never had car seats as legally they don’t need to. You could always ask the school what the route is and I guess it depends on where they are going as to what route they take.