It's a special exhibit on the study of popular culture. However, somehow, they decided this means robots! The exhibit features a number of real robots, including a Baxter and several that you can teleoperate to pick up blocks and things, as well as toy robots through the ages, as well as fictional robots. It also includes one of the original DeLorians from the Back to the Future movies. My four year old really enjoyed it.
MOS is open until 9pm on Fridays and has a reasonably nice cafeteria on sight with a great view of the Charles River.