Don't do it, Finnish. Keenan's right. I would hate to have a knock break or a string come off a child's bow. It was a good idea as far as thinking of a precautionary measure against breaking the bow, but it puts the child's safety potentially at risk. Besides, it's trying to compensate for a lack of competency on the part of the child by purposely implementing a defect in the bow (the string slips off). Better to just work with the child, when they are old enough to grasp the teaching, to not overdraw the bow.
JMHO
~~Papa Matt