Final answer:
Parents should introduce solid foods to an infant's diet at 4-6 months of age, when the infant exhibits readiness for solid food, such as being able to sit up and being interested in solid foods.
Step-by-step explanation:
The nurse should instruct parents to introduce solid foods in an infant's diet at 4-6 months of age. At this stage, infants are typically able to sit up with support and may show interest in solid foods. They also develop the ability to move food from the front to the back of the mouth to swallow. At around six months, babies also begin teething, which can indicate readiness for more textured foods. It is important for parents to recognize that every infant is different, and while the 4-6 month range is typical, some infants may show signs of readiness a bit earlier or later. The disappearance of the rooting reflex, which usually occurs around 4 months, is indeed a sign that an infant may be ready for solid foods. However, this does not mean solid foods should be introduced as soon as the reflex disappears. Introducing solids before 4 months is not recommended as infants' digestive systems are not yet mature enough. It's also irrelevant to wait for the first tooth to erupt before introducing solids, as teeth are not necessary for an infant to move to solid food. The general guideline, therefore, falls in the 4-6 month range, supported by developmental milestones and physiological signs of readiness.