The psychologist Jean Piaget developed his Theory of Cognitive Development to describe the stages in which children are able to develop awareness of their environment. Piaget's theory of Cognitive Thinking describes a child's ability to make decisions as these relate to persons and objects within their field of vision. The development of cognitive thinking occurs in stages and the first stage which starts from birth through the age of two is called the Sensorimotor period.
An infant's first 6 weeks (Reflexive stage) is a period of "sensing." An infant learns of his environment by sucking almost everything within his reach or upon discovery, his own hand. As the infant becomes aware of people and nearby objects, he reaches, grabs and sucks on these as part of his "learning process." Such actions are repetitive ("Circular reactions") in infants between 2 and 4 months old. It is therefore extremely important that objects within an infant's field of vision are made larger than an infant's mouth or the diameter of it's throat to avoid the potential for swallowing and/or choking on found objects. For the same reason, such objects cannot have sharp edges and points.
The Consumer Products Safety Commission advises that objects more than 2 inches in diameter are less likely to be swallowed. The Commission developed a "small parts cylinder" or "choke tube" which has an opening similar to the diameter of a 2-year old's throat. Objects that fit within the tube's opening would be considered a "small part" and therefore should not be given to infants.
It should also be noted that when an infant discovers an object that it cannot readily suck, it will continually touch and rotate the object within it's hand. This finger-twirling action, common among those betwen the ages of 4 through 8 months; suggests that the infant has found a toy. Such small parts which now have "play value" need to be firmly attached to it's larger part or else it can detach and potentially becomes a choking hazard. Should it be necessary for large toys or garments to contain "small parts" like buttons, bows and zipper pulls for functional reasons; such "small parts" need to withstand at least 15 pounds of pulling force held for at least 10 seconds. This is the pulling strength of a toddler.
The period that children place objects in their mouth extends through the age of 3 years then gradually diminishes and ends at about the age of 5. It is very important that small parts are either avoided or firmly attached to larger objects because infants and young children have not developed a level of cognitive thinking that allows them to reverse a harmful situation. According to Piaget, the ability to reverse an action is not possible until the child reaches the age of seven.