Experts have found out that the child usually begins to recognize sarcasm in the speech of other people at the age of eight or nine years - but only the tone. He picks up the discrepancy between how sounded words and their content, feels that his voice was "something wrong" - for example, when a person, being in a terrible situation, exclaims: "Oh great!" About the same mechanism allows you to capture the intonation babies do not understand the words - some saying they scare some calm and some are annoying.
When the eight-year child hears ironic comment, uttered in a neutral tone, or get any other way, do not convey the tone, you can not catch the sarcastic notes, even if they are obvious to adults. Only eleven years to twelve he begins to recognize sarcastic remarks without audio prompts.
In addition, studies have shown that the ability to recognize the irony and sarcasm are closely linked to the ability of empathy. The man who can catch the barb in a speech interlocutor, and can better understand his way of thinking, and emotional state.
It is known that the ability to capture the subtext in the speech of other people depend on specific brain functions. Patients who after an injury of some parts of the brain lose the ability to empathize, losing with it the ability to understand ironic statements.
With regard to children - for their sarcasm just a new concept, which still need to learn how to use, and it takes time.