Asked by researchers to sort objects by shape, most toddlers in a large study had no trouble doing so  When subsequently told to sort by color, the toddlers seemed to have difficulty following the new rule and almost invariably persisted with their first approach  The researchers suggest such failures to adapt to new rules often result from insufficient development of the prefrontal cortex in toddlers
The cortex is essential for functions like adapting to new rules, yet is slow to mature, continuing to develop right into adolescence
Certain kinds of behavior on the part of toddlers may not be willfully disobedient.