Final answer:
The nurse should report the WBC count of 3,000 to the provider, as it can indicate a compromised immune system and a risk of infection in a child with acute nephrotic syndrome receiving prednisone.
Step-by-step explanation:
The lab finding that should be reported to the provider for a child with acute nephrotic syndrome receiving prednisone is a white blood cell (WBC) count of 3,000. This is because a low WBC count can indicate a risk of infection, which is a concern in patients treated with steroids like prednisone. The other findings listed, such as a sodium level of 142, potassium level of 4, and platelet count of 298,000, are within normal ranges and do not indicate an immediate concern in the context of nephrotic syndrome treatment.