Dr. Kacie Flegal, a pediatrics chiropractor, claims a positive correlation between keeping toddlers and babies barefoot and intelligence.
The logic behind this statement is that children need to fully exercise their sensory systems. Walking barefoot actually accomplishes this.
When a baby walks around barefoot, many systems are asked to contribute to the motor task, such as the vestibular and propriceptive systems.
The idea, here, is to maximize the amount of input the body receives. Therefore, neural networks develop.
Although other parts of the body can be of use to stimulate both the vestibular and proprioceptive systems, it could be that feet are more relevant because they are loaded with nerve endings and other cells responsible for sensory input.