Round Dining Tables Are More Casual
Rounded tables hearken back to Arthurian legends in which a round table was used so that no one was put in a position of greater importance than another. This is very fitting when you consider the much more casual dining environment that most modern families enjoy. This is also why you will see round tables used more often in restaurants where social interaction is encouraged.
In the case of small round dining tables, it creates a more acute sense of intimacy than you would experience with a square table. Whenever there is a scene of a romantic dinner between two people, it almost always takes place at a small, round dining table rather than at a square one.