Final answer:
The most suitable action for the APRN is to refer the child to a pediatric endocrinologist since the symptoms are indicative of a potential vitamin D deficiency affecting bone development, likely rickets. An endocrinologist can further investigate and diagnose the condition, after which treatment options such as supplementation can be considered.
Step-by-step explanation:
The most appropriate action by the Advanced Practice Registered Nurse (APRN) for a 3-year-old male who presents with short stature, bowed legs, and hypotonia is to refer the child to a pediatric endocrinologist. These symptoms may suggest a condition such as rickets, which is characterized by improper bone development in children due to malabsorption of calcium and a deficiency in vitamin D. Given that rickets affects serum phosphate levels, further investigation by an endocrinologist into the child's hormone levels and bone metabolism is warranted to confirm the diagnosis and plan appropriate treatment, which may include vitamin D and calcium supplementation.