what if they refuse to leave and continue to be disruptive?
Policy in every district I've worked in is this when faced with a disruptive student who will not obey instructions:
1. Pull over and put on 4-ways. Secure the bus, turn off engine, remove key into your pocket.
2. Call in to base, request the police assistance.
3. Keep door locked and let no one off if possible.
4. Wait for police to arrive and remove the child. No children get off the bus for ANY reason (save for a weapon being brought into play or the safety of others), even if their parents show up till the authorities are present.
You have a secondary option if the child is just being disruptive but sitting safely to return to the school to have school officials remove the child and wait for the parents. You can not put a child off the bus once they are on, except at their stop or at school for any reason.
If the child attacks you, and it IS a possibility, you may defend yourself as far as to stop the assault and with the greatest restraint. You are never to touch the child unless your health and wellbeing is threatened. Not even if they attack another child. If the child leaves the bus by a window or back door, report to the police what happened. Always keep dispatch appraised of what is happening.
If a child is being disrespectful to your authority, separate them if possible from other children up front. Move other children away from them if possible. If the child is inciting others, call dispatch for advice or police assistance to deal with threats to the safe operation of the vehicle. Make sure to put on your report everyone involved in the problem so the school can punish them properly with detention, suspension or expulsion.
I've had to resort to a few of these tactics to get a bus under control and thankfully never had to have cops called, but school officials have shown up and hooo boy those kids were scared of them showing up miles from school and the kids started to tattle on the troublemakers.