Indeed such aiguillette was worn, for example at the "Grosses Militär-Waisenhaus" at Potsdam.
It had a different form with tips and was worn over the right shoulder.
Practically always such indication was worn for the function of "Zugführer vom Dienst". When
one was worn without the tips then it reflected the "Jungmann vom Dienst".
As Garry says it is possibe the boy shown has such a function at a training-course or camp.