Final answer:
Children, compared to adults, have a proportionately large head, which is evident when comparing anatomical proportions between newborns and adults.
Step-by-step explanation:
Compared to adults, children have a proportionately small head. During infancy, a newborn's head, including the cranium, is significantly large relative to the rest of the body. In contrast to this, an adult's head is a much smaller fraction of their total body length. This is a characteristic feature seen in the development of humans as they grow from infancy through childhood and into adulthood.
Answering the student's options in order, children have: a) smaller airways compared to adults, not larger ones; b) their skin is indeed thinner; c) they have a smaller muscle mass; d) and as emphasized, they have a proportionately large head. As depicted in developmental biology texts, the size difference in the head proportion is visually evident when comparing the anatomical drawings of a newborn and an adult.