I have had several parents who say that their children don't want to wear a seat belts, will object to doing so and therefore won't be doing so. I've not had to deal with these parents myself, only support my colleagues handling of the situation. The worst we ever had were a group of siblings who would not do as they were told by their au-pair. The four were aged between 6 and 16 and each one was a miserable little sh!t. They were denied boarding on the last flight to their destination, having been kicked off two other flights. Wealth meant that they would in future have to charter their own aircraft as they certainly won't be flying with us agian.
PM