How does it prepare you for employment? What are the real benefits of an internship? How many should a computer science major have?
My experience is not only circumscribed to the Brazilian market, but is also highly personal. So it is not a general recommendation.
That said, I regret a lot not taking internships. I focused a lot more on the academics. Sadly, I discovered I could learn a lot of things, a lot earlier, by entering the marketplace. You learn to solve more concrete problems, how to work with colleagues, how to value the customer needs etc. And you learn all of it a lot quicker!
Here, one internship is enough, since there is a shortage of developers. (Other areas are not that lucky.)
Note, however, that it is specific to my marketplace. here, for example, internships are required by law to be paid. For all I would learn, I do not think it would be worth it to work for free. Also, it may be the case your academic course is much more useful than mine. Anyway, I still suspect being a paid intern is a great decision.