On “Friends,” Richard’s son whom Monica kissed on Thanksgiving was Tim Burke. Tim appears in the season-four episode “The One with Chandler in a Box,” when Monica invites him to Thanksgiving dinner after meeting him through her father’s connection to Richard Burke.
The situation is awkward because Richard was Monica’s former boyfriend and was also a longtime friend of her parents. Monica initially treats Tim as a possible romantic interest, but the resemblance to Richard and the uncomfortable family connection quickly make the relationship seem inappropriate. After Monica kisses Tim, she realizes the situation is far too strange and ends the encounter.
Tim Burke was played by Michael Vartan, who later became known for roles in Alias and other television and film projects. The episode is also remembered for Chandler’s punishment after kissing Joey’s girlfriend, Kathy: Chandler spends Thanksgiving inside a wooden box. The full character name is Timothy Burke, but “Tim Burke,” the form used in the question, is the standard answer.