Q: When I try to explain to my three-year-old the reason why we have certain rules (like no touching the TV) or why we can't go to the park right now, and she will just throw a tantrum. Other times she goes along with rules or transitions with no fuss. Why the difference?

A: Between approximately 2 and 3, children begin to understand the logical connection between ideas, which is the reason they start to ask “Why?” about almost everything!  It is a major milestone in their overall development and in their understanding of how the world works. 

However, this stage can also be very confusing and exasperating for parents. The inconsistency you’ve described in your daughter’s behavior is a perfect example and is due to the fact that 3-year-olds’ grasp of logic is still pretty shaky. One minute they seem very reasonable and wise and the next act totally irrational. This is coupled with the fact that 3-year-olds are still working hard on managing their strong emotions which can interfere with, and often trump, their ability to act as rational beings.