Final answer:
Parents of a child with Tetralogy of Fallot should contact healthcare provider immediately if the child becomes pale, cool, and lethargic, due to potential urgent cardiovascular or oxygenation issues.
Step-by-step explanation:
If a 2-year-old toddler with Tetralogy of Fallot becomes pale, cool, and lethargic, the best immediate action for the parents to take is to contact their healthcare provider immediately. Tetralogy of Fallot is a congenital heart defect that includes four anomalies, but these symptoms specifically might indicate a cardiac event or low blood oxygen levels that need urgent medical evaluation and treatment.
It is important to note that while providing a quiet environment or encouraging fluid intake can be supportive, these measures should not delay seeking professional medical care, as prompt intervention is critical for the safety and well-being of the child.