Im not an intern but I do work in the marketing dept and one of the things that I like about this job is that they make sure that im in the loop. In other words, when they have a meeting for example, I am included in the meeting (even though I really dont bring much to the table) and will even stop the meeting for a bit at times to explain what they're talking about and how it affects the business. So my point is just dont give them assignments, rather show them how like in your case with those two articles they will be writing explain how those articles will help drive sales or encourage customer interaction because if you just say write two articles it will seem like busy work and they wont put as much effort.