Field open to all students

 I believe that the school field should be open to all age groups, if the excuse is that anyone can enter the field, why are year 7s one of the year groups with access to the field? surely they are most at 'risk of the public'. If one of the reasons is that all students on the field at the same time is too many to keep an eye on, then i suggest that access to the field rotates on a daily basis between year groups (2/3 year groups on the field per day). The whole concept of the year 7s being allowed on the field baffles me