Whoever said television destroys the brain obviously hasn't seen any shows geared towards preschool kids. There are many shows on PBS, NickJr, and Playhouse Disney that offer educational shows, leaving your toddlers ready for preschool even before the first day!
CommonSenseMedia.org has made a list of the Top 10 shows for Preschoolers in the last decade, which includes - Dora the Explorer, Imagination Movers, Stanley, The Wiggles, Little Einstein, and WordGirl. I'm a bit surprised that Sesame Street isn't on the list, but the shows listed are great learning tools nonetheless. Take, for example, WordGirl. She's put into situations where she must use the English language to solve her problems, and this will not only will entertain your toddler, but educate them along the way.