Final answer:
The most appropriate nursing response is to ask the caregiver to share more about their feelings, providing a supportive and non-judgmental environment.
Step-by-step explanation:
When responding to a caregiver who feels guilty about a child ingesting a caustic substance, a nurse should provide empathetic and professional support. The most appropriate response would be, "Tell me more about your feelings." This opens a dialogue that allows the caregiver to express their emotions and concerns, thereby starting the process of emotional healing. It is also important to reinforce the need for safety and supervision, but in a non-accusatory manner. Bringing up actions like ensuring household chemicals are locked up and understanding how to respond during emergencies with children, without direct blame, can be educational and preventive for future incidents.