**Core Concept**
The distribution and proportion of Intracellular Fluid (ICF) and Extracellular Fluid (ECF) change significantly from childhood to adulthood, primarily due to variations in body size and composition.

**Why the Correct Answer is Right**
As individuals mature, their body size increases, leading to a proportional increase in total body water (TBW). However, the proportion of ICF to ECF changes, with ICF making up approximately 40% of TBW in adults compared to 60% in children. This shift is largely attributed to the growth of muscle mass, which contains more ICF, while the proportion of ECF remains relatively constant. The adult ECF compartment is primarily composed of plasma and interstitial fluid, with a volume of approximately 12-15 liters.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because there is no significant change in the proportion of ICF to ECF from childhood to adulthood. The ICF to ECF ratio is relatively constant across age groups, with some variation due to changes in body composition.
**Option B:** This option is incorrect because the proportion of ECF to ICF increases from childhood to adulthood, not the other way around. The ECF compartment remains relatively constant in size, while the ICF compartment increases in proportion to the growing body size.
**Option C:** This option is incorrect because there is no significant change in the volume of ECF from childhood to adulthood. The ECF compartment remains relatively constant in size, with some variation due to changes in body composition.

**Clinical Pearl / High-Yield Fact**
Remember that the ICF to ECF ratio changes from childhood to adulthood, with ICF making up approximately 40% of TBW in adults compared to 60% in children. This knowledge is essential for understanding fluid balance and distribution in different age groups.

**Correct Answer: D.**