ur discrediting them that they may have requested tasks but maybe ignored by their lead and with no working experience & social experience they were afraid to approach their manager as it would bring trouble to their lead which in turn set trouble among themselves?

if u are the manager, you should keep at least a weekly update from the lead and from the interns, not just sit there and assume they are alright like Tom Cruise in Top Gun.

if no tasks were given to interns u should be able to tell by shooting few simple questions, then you call the lead in and ask him to explain why the interns aren't improving.

i can tell you most leads aren't interested in training interns because they aren't part of the fulltime team and they know they will most likely leave after finishing their internship and they know in such short time it's hard to train them to be actually helpful, so they are deadweight, might as well let them rot and focus on own work.

if the lead is Indian Expat, expect even worse.

why not u request from ur line manager to get more task other than facebook?

also letting intern handle fb is like letting ur youngest sibling represent the whole family. abit risky from company image POV.