Final answer:
Poor diet depresses the immune system, making children more susceptible to diseases, while diseases can also worsen nutritional status, creating a harmful cycle. Vitamin A deficiency is one example that specifically impacts immune system development and increases infection risk.
Step-by-step explanation:
The relationship between poor diet and susceptibility to childhood diseases is complex. Undernutrition can depress the body's immune response, leaving children more vulnerable to diseases. This weakened state from poor nutrition can increase the likelihood of contracting infections and can also exacerbate the severity of diseases that children do contract, such as measles and chickenpox. On the other hand, diseases can also lead to reduced nutrient intake or absorption, thus creating a detrimental cycle. Vitamin and nutrient deficiencies, like that of vitamin A, hold particular significance as they are crucial for the development of a robust immune system and can lead to an increased risk of infection and other health issues.