I fall on the 'its public transport' side of things and sometimes, despite parents' best efforts, children will make noise (as do adults). So long as parents make a best efforts basis to keep them calm and under control, good enough for me.

Re suggestions of limiting children to cheaper cabins as those in posh seats are trying to sleep / work. It's already hard to sleep / work in the back. How about banning children from economy, so those in the seats have a chance to sleep best they can, and limiting them to business and first where comfort of lie flats and free flowing booze can offset the noise!