Children are extremely perceptive and absorb what goes on around them long before they can talk or even comprehend language. They are like finely tuned receivers that pick up much more than is merely said. They are receptive and attuned to every mood, feeling, and change that goes on in people around them.
Sometimes the routes leading to feelings of anger are so convoluted and circuitous that it takes enormous skill to discern their original source, or fountainhead. But regardless of the reason for or the source of the anger or the relative ease or complexity in perceiving either the anger or its source - everybody, but everybody, gets angry.