Answer:
It is useful to account for the age range we are talking about. If we are taking about school going children, It should be taken into account that if the environment in question has any hazards, such as any exposed wires or a slope too steep that it can cause injuries or a weather prediction of high tide when preparing for an activity on the beach or seaside.
Another good measure is to look into the ratio of 'students/people for whom the activity is being planned for', to 'the volunteers or teachers that are helping them', to understand if the number each volunteer is responsible for is reasonable and manageable. It would be preferred these helpers can come together before the activity and own responsibility for particular children so every child is given adequate attention.
It should also be made sure that the place is cleaned of any garbage of animal waste or any infectious fly or animal. Anything, be it furniture or necessary equipment, having sharp edges or nails should be indefinitely removed once its use under the supervision of an expert is over.
At last, to make the activities full of learning and meaningful , the assignments and activities must be planned and have assigned objectives, so best use is made of resources and healthy and safe use is maintained.