John Barach observes that even though today, families eating together is seen as the ideal, something to be aspired to, it wasn't always thus. Citing various sources, he notes how in the ancient world, the idea of a family meal and especially of children being present at the table, is largely absent. Here is a sample quote:
The overriding impression … which the sources leave — the prevailing ideology one might say — is that no matter whether modest or elaborate, dinner was a meal about which the individual male made an individual decision — to entertain, to eat alone, to respond to an invitation — in a world in which ties of amicitia and hospitium were paramount. Other household members, wives for example, responded to such decisions as appropriate. Dinner was not a meal at which the company of family members was automatically and invariably assumed essential or even desirable. Within innumerable elite households, therefore, many wives and children must have eaten completely apart, in time and place, from their husbands and fathers, and from one another … and when husbands, wives and children did dine together, they did so in ways that continually reinscribed the subordination of the two latter to the former (“The Roman Family at Dinner,” in Inge Nielsen and Hanne Sigismund Nielsen, Meals in a Social Context: Aspects of the Communal Meal in the Hellenistic and Roman World [Aarhus University Press, 1998], 49).
So what caused the change? Read the answer here