I've transported kids in the back of a cop car. Once is usually enough. I've transported kids in the back seat of our crew cab paramedic trucks. I saw a crew bring a 700# male in in a department utility truck with a lift gate. I'm guessing people have been hauled in a fire engine on my department. I never did it but wouldn't hesitate if there wasn't any other option and the need was critical. I don't think anybody on my job would say anything other than good job.