Not at all. Cropping too close would make it kind of boring - the negative space at the edges sets them off from their surroundings/brings them into sharper focus and makes the composition more dynamic.
When cropped the elbows would give me a feeling that the boys were pushing away the boundaries of the frame. As if they need more space for growing minds, wishes and bodies.
Great shot, very well composed. May I suggest you that next time you are in a situation like this try to ask your subject-model to leave the mouth closed,even if their are smiling, as you can see, the strongest personage in the photo is the one with the mouth closed.