A child presents with Class III malocclusion. Which of the following habits is LEAST likely to be a contributing cause?

Class III malocclusion is primarily associated with genetic predisposition (mandibular prognathism or maxillary deficiency), mouth breathing (which can contribute to a narrow maxilla and anterior open bite), and tongue thrust (which can push the lower anterior teeth forward). Digit sucking (thumb or finger sucking) is primarily associated with Class II malocclusion and anterior open bite — the sucking forces push the maxillary incisors forward and restrict normal mandibular development, which would create a Class II relationship, not Class III. Therefore, digit sucking is least likely to contribute to Class III malocclusion.