Children need to know where to go and who to contact in an emergency. It could be that you are temporarily separated. Doesn’t really matter. Someone needs to be in place with a prearranged plan, something simple to do and with backups in case the first options fail. Teach them not to panic and think it through. They should not listen anyone being stupid when it feels wrong.
They could be at school expecting you to pick them up and your car breaks down. When everyone has left the building and area what do they do?