If you ignore a risk assessment you'd be in serious shit surely,would probably be dobbed in by somebody running to the press reporting school children not being looked after properly on trips.
Oh and as a mother of a child who had an accident on a bus when dd ended up flying under several seats after breaking and a near nasty one with the 3 dc on a train standing up when no adult would give my obviously poorly 6 year old a seat even for 5 mins during a 40 min journey(it goes both ways)I think you'd be foolish to take any risk with other people's children in a professional capacity.
Times have changed.Childminders have to right risk assessments on their own living rooms.If they're not up to scratch they aren't allowed to work.