Google  has two CS internships: the Software Engineering Internship here:

https://www.google.com/about/careers/search#!t=jo&jid=132795001&

And the Engineering Practicum Internship here:

https://www.google.com/about/careers/search#!t=jo&jid=120165001&

The difference is that the practicum internship is specifically geared towards freshman and sophomores who may not have as much experience in upper-level CS courses.  They get a lot more mentorship and training.  Freshman and Sophomores can and should apply to both positions.  Juniors can only apply to the default internship.