NEW : It was carrying 52 people : two drivers , four other adults and 46 children , aged 11 and 12 years old . The bus was not speeding at the time of the crash , a Swiss prosecutor says . NEW : The impact was so great that their seat belts did not save the children , he says . Belgian Prime Minister : " I am shocked by this accident and deeply saddened to learn about it. The bus was returning to Belgium from a ski trip with 52 people aboard , most of them children .
NEW : The bus was not speeding at the time of the crash , a Swiss prosecutor says . NEW : The impact was so great that their seat belts did not save the children , he says . Belgian Prime Minister : " I am shocked by this accident and deeply saddened to learn about it. The bus was returning to Belgium from a ski trip with 52 people aboard , most of them children .