Final answer:
The nurse's best advice for introducing solid foods into a child's diet is to introduce one solid food at a time, several days apart.
Step-by-step explanation:
The nurse's best advice for introducing solid foods into a child's diet is to introduce one solid food at a time, several days apart. This allows the mother to observe any potential allergies or reactions the child may have to a particular food. By introducing one food at a time, the mother can also monitor the child's tolerance and acceptance of different solid foods.