I do the old-school thing of buying shows by episode on iTunes for this particular reason (even if the shows are available for "free" in Netflix or Amazon). My kid gets one new episode per week, and she only watches from the iTunes library, which is a self-throttle because it gets boring after a while because it's the same set of episodes. She also learns more from every show and can remember the name of species and their habitats etc way better because she has watched most shows dozens of times after some time.