Final answer:
Toddlers lack the anteroposterior curves of an adult.
Step-by-step explanation:
The true statement about the appearance of a toddler's body is that toddlers lack the anteroposterior curves of an adult. During infancy, toddlers have a relatively straight posture without the distinct curves in their spine that adults have. As they grow and develop, these curves gradually develop, such as the cervical curve in the neck region and the lumbar curve in the lower back. It is important to note that the other statements mentioned in the question, including a concave-shaped abdomen, slightly inverted feet, and a gap between the legs while walking, are not true about the appearance of a toddler's body.