Final answer:
The family member's understanding that they need to check the child's pulse for a full minute before administering digoxin and their knowledge of the proper action if the heart rate is too low indicates effective teaching.
Step-by-step explanation:
A statement by the family member that indicates effective teaching on how to check a pulse for a preschooler taking digoxin might be: "I understand that we need to check the child’s pulse by placing our fingers on his wrist or neck and count it for a full minute before giving the digoxin. If his heart rate is below the threshold the doctor provided, we will not give the medication and will call the healthcare provider immediately." This demonstrates they have grasped the importance of monitoring the heart rate and the appropriate action to take if it’s too low, which is critical with digoxin therapy to avoid toxicity since it affects the heart rate.