A mother brings a 23-month-old child for a well-child check. She apologizes, stating, “It’s my allergies, not a cold, that is causing me to sniffle so much.” The mother reports that the toddler seems “slower at doing things” than her older children did. The nurse notices that the child sits in the mother’s lap without fear or hesitation and responds to the mother’s questions, but fails to look at the mother’s face when being spoken to. These behaviors are supportive of what additional assessment?