Neuroscientists and philosophers agree that people grossly overestimate how much they can consciously choose. Much of the time we believe we are making a free choice when we are actually compelled by inner forces. Mostly we take action and then think about what we are doing - a split-second later - not vice versa.
We are often left with the false impression that our thoughts have spurred our impulses and we have made a conscious decision, when in fact our impulses have spurred our thoughts. So we reach for a glass of water and then think about being thirsty, but we think we have decided to take a sip of water. Our bodies are consistently responding automatically to triggers whether we think of them or not. This is equally true whether we are reaching for a glass of water or responding to an insult.
Not only children grapple with impulsivity. It is part of human nature. As we mature, we become better at handling our impulses, but only some of them. We cannot be aware of all we do because we can only pay attention to a small amount of our activity. Inevitably, we all might do something we regret. We might shoot someone a dirty look or raise our voice without wanting to reveal our anger. Or grab a cookie without giving ourselves permission first. Becoming aware of how we operate gives us a leg up on trying to deal with our nature.