The infant child of the Governor of New Ozai, Tom Tom is a mischievous boy.  He caused Momo a lot of pain, and forced an unnecessary encounter between Aang and Azula, Ty Lee and Mai.  His father thought he was kidnapped, when really he was just taken out of the city by accident.

When Momo was trying to get some Fire Flakes, Tom Tom began to harass the winged-lemur.  He kept pulling his tail, and like many animals, Momo doesn't like to have his tail pulled on.  Also, Tom Tom was accidentally taken out of the city by mistake when the Resistance was led out for "Pentapox."  The result was a trade: King Bumi, a powerful Earthbender King, for Tom Tom, a young, defenseless boy.  At the last minute, however, Mai backed out of the deal, on Azula's advice.  This forced a fight between Aang, Katara and Sokka and Azula, Mai and Ty Lee.

At the end of "Return to Omashu," Aang quietly returned Tom Tom to his family, after the deal fell through.  His parents were certainly glad to see him again, and probably won't let him out of their sight until he turns 48.