First for Schools Speaking part 2
"With the Cambridge English First for Schools Part 2 task, one of the key skills in keeping going in talking about the photographs is not just to describe observable details but to situate these details in terms of the wider context of the situation i.e. speculating as to what lies behind the picture."
This means you shouldn't just describe what you see in the picture but talk about what might be happening around the point the picture was taken.
Here, you would need to use language of possibility and probability e.g." The children may be students on a school outing. They seem to be excited about what they are about to do..." etc.