The reasons are below. Compared to the adults. Most adults intuitively recognize a child at a distance because children's body proportions are very different from those of the adult. The head and torso of the infant are proportionally much bigger than the limbs compared to an adult. This means that the working parts of the child occupy a much greater proportion of the body accounting for a baby's higher metabolism.
Babies breath more frequently, and the heart beats much faster than in an adult.
These factors contribute to the infant's relatively greater requirements for food and fluids. Any dietary intervention has more powerful and serious effects on the young child. Similarly, when illness interrupts feeding, babies get into trouble much more quickly. A lot of this has special implications for the health care system. Society is intuitively more nuturing of babies precisely because they are more fragile.