Final answer:
The initial sign of nephrosis that a nurse might note in a child is proteinuria, which occurs due to damaged glomeruli in the kidneys.
Step-by-step explanation:
An initial sign of nephrosis (nephrotic syndrome) that a nurse might note in a child is proteinuria. This condition is characterized by the presence of an abnormally high amount of protein in the urine due to damaged glomeruli within the kidneys. Signs such as edema, low serum albumin, and high cholesterol are also frequent features of nephrotic syndrome.